If. 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


OF 


Class 


.. 


THE  ASSAYER'S  MANUAL. 


AN  ABRIDGED  TREATISE 


ON    THE 


DOCIMASTIC  EXAMINATION  OF  ORES,  AND  FURNACE 
AND  OTHER  ARTIFICIAL  PRODUCTS. 


BY 

BRUNO    KEEL, 

PROFESSOR  IN  THE  ROYAL  SCHOOL  OF  MINES  J   MEMBER  OF  THE  ROYAL  TECHNICAL  COMMISSION 
FOR  THE  INDUSTRIES,  AND  OF  THE  IMPERIAL  PATENT  OFFICE,  BERLIN. 


TRANSLATED  FROM  THE  GERMAN 
BY 

WILLIAM  T.  BRANNT, 

EDITOR  OF  "THE  TECHNO-CHEMICAL  RECEIPT  BOOK,"  ETC. 

SECOND    AMERICAN    EDITION. 
EDITED  WITH  EXTENSIVE  ADDITIONS 

BY 

F.  LYNWOOD  GARRISON, 

MEMBER  OF  THE  AM.  1NST.  OF  MINING  ENGINEERS,  FRANKLIN  INSTITUTE,  AND  ACADEMY  OF 

NATURAL   SCIENCES,    PHILADELPHIA;    FELLOW   OF   THE   GEOLOGICAL   SOCIETY 

OF  LONDON  ;   MEMBER  OF  VEREIN  DEUT8CHER  EISENHUTTENLKUTE 

AND  IRON  AND  STEEL  INSTITUTE. 


ILLUSTRATED    BY    EIGHTY-SEVEN    ENGRAVING^ 

4% 

UNIVERSITY 

CF 

PHILADELPHIA  : 
HENRY   CAREY   BAIRD   &   CO., 

INDUSTRIAL  PUBLISHERS,  BOOKSELLERS,  AND  IMPORTERS, 
810  WALNUT  STREET. 

LONDON: 
E.  &  F.  N.  SPON,  125  STRAND. 

1889. 


/\|  D Q  U 


COPYRIGHT  BY 

HENRY  CAREY  BAIRD  &  CO., 

1889. 


COLLINS  PRINTING  HOUSE, 

705  Jayne  Street. 


PREFACE  TO  THE  SECOND  AMERICAN  EDITION. 


THE  first  American  edition  of  KEEL'S  ASSAYER'S  MANUAL 
has  met  with  so  much  success  that  it  has  been  determined  to  issue 
a  second,  containing,  in  addition,  numerous  and  approved  assay- 
ing methods  which  have,  since  the  appearance  of  the  first  edition, 
been  introduced.  Although  there  have  been  many  improvements 
in  the  apparatus  used  in  assaying,  it  seems  hardly  the  province  of 
a  work  of  this  kind  to  constitute  itself  a  catalogue  of  such  appa- 
ratus. Only  a  few  of  the  most  notable  of  these  novelties  have 
therefore  been  mentioned.  With  the  exception  of  the  omission 
of  the  English  equivalents  of  the  weights  and  measures  but  few 
and  unimportant  changes  have  been  made  in  the  old  text.  The 
use  of  the  metric  system  has  become  so  universal  amongst  chemists 
and  assayers  in  this  country  that  the  insertion  of  English  equiva- 
lents was  thought  unnecessary  and  confusing.  In  the  Appendix, 
however,  there  will  be  found  tables  of  the  relative  values  of  the 
metric  and  English  weights  and  measures. 

While  there  has  been  but  little  improvement  in  the  old  fire 
assay  methods  the  advancement  in  wet  and  particularly  electro- 
lytic methods  has  been  notable.  In  this  particular,  the  Editor 
has  drawn  largely  from  Balling's  Fortschritte  im  Probirwesen 
(1887).  The  entire  chapter  on  Tungsten  was  translated  from 
that  work,  and  it  might  be  observed  in  this  connection  that  it 
is  believed  that  the  element  tungsten  has  never  before  been 
treated  at  length  in  any  work  on  assaying.  Although  Keii  has 


IV  PREFACE   TO   THE   SECOND   AMERICAN   EDITION. 

confined  the  assaying  of  iron  to  a  separate  work  on  that  subject, 
it  has  been  deemed  expedient  in  this  case  to  prepare  and  insert 
in  the  Appendix  a  somewhat  lengthy  article  on  the  Dry  Assay 
of  Iron  Ores. 

The  Editor  here  desires  to  express  his  thanks  to  a  number  of 
his  professional  friends  for  assistance  in  preparing  this  work,  and 
he  feels  under  special  obligations  to  Prof.  Richard  Smith  of  the 
Royal  School  of  Mines,  London ;  Dr.  Edgar  F.  Smith  of  the 
University  of  Pennsylvania;  and  Prof.  R.  H.  Richards  of  the 
Massachusetts  Institute  of  Technology. 

The  portions  of  the  volume  contributed  by  the  present  Editor 
are  inserted  in  smaller  type  than  the  text  of  Kerl.  In  some  in- 
stances foot-notes  to  the  original  matter,  added  by  the  Editor,  are 
inclosed  in  square  brackets,  thus,  [  ].  These  arrangements  of 
matter  will  show  at  a  glance  who  is  responsible  for  any  statement 
in  the  book. 


F.  LYNWOOD  GARRISON. 


"  CHEPSTOW,"  RADNOR, 
DELAWARE  Co.,  PA.,  April  25,  1889. 


AUTHOR'S  PREFACE. 


THE  object  of  the  "  Assayer's  Manual"  is  to  give  directions  for 
executing  docimastic  tests  of  natural  and  artificial  products  by 
methods  taken  mostly  from  practice,  and  which  are  of  interest 
especially  to  metallurgists,  but  also  to  other  technologists.  To 
those  possessing  some  knowledge  of  chemical  and  docimastic 
manipulations,  the  aphoristic  mode  of  expression  I  have  chosen 
will  be  sufficiently  clear  to  enable  them  to  execute  the  tests  with- 
out further  instruction.  Those  less  skilled  are  referred  for  details 
to  my  larger  work  on  "Assaying,"  Leipzig,  1866.  Copious 
bibliographical  references  are  given  in  the  foot-notes,  which  are 
calculated  to  help  both  the  teacher  and  scholar. 

As  the  assaying  of  iron  has  been  thoroughly  treated  in  my 
manual  of  "Assaying  of  Iron/7  Leipzig,  1875,  the  subject  has 
been  omitted  in  the  present  treatise. 

B.  KERL. 

BERLIN,  September,  1879. 


CONTENTS. 


GENERAL  DIVISION. 

PAGE 

Object  of  the  art  of  assaying ;  The  dry  method ;  The  wet  method ; 

Precipitating  metals  by  electrolysis 17 

Volumetric  assays ;  Colorimetric  assays ;  The  blowpipe       .         .         .18 

I.     MECHANICAL  MANIPULATIONS. 

Sampling;  Non-alloys;   Substances  in  fragments         .         .         .          .18 
Homogeneous  fragments  ;  Samples  from  the  heap  ;  Samples  taken  while 

the  ore,  etc.,  is  being  weighed ;   Samples  by  rasping;   Slag  samples  ; 

Heterogeneous  fragments;  Sampling  by  the  cross  method  .  .  19 
Sampling  by  dropping  the  ore  ;  Small  ore  and  pulverized  substances ; 

Sampling  while  weighing  ;  Samples  of  goldsmith's  sweepings  .  .  20 
Sampling  before  weighing ;  Substances  in  a  state  of  fusion  .  .  .  21 
Alloys;  Sampling  by  cutting;  Samples  from  refined  Upper  Harz 

silver 22 

Sampling  by  boring  ;   Sampling  by  dipping ;  Sampling  by  granulation  ; 

Samples  for  producing  coins    ........       23 

Preparation  of  the  sample  ;  Determination  of  moisture ;  Water-baths ; 

Fresenius's  drying  disk,  illustrated  ......       24 

Pulverizing  the  desiccated  mass  ;   Sifting 25 

Washing;    Schulze's  washing   apparatus,    illustrated;    Iron  vanning- 

shovel,  illustrated ;  Mariotte's  bottle        .         .         .         .         .         .27 

The  art  of  vanning  ;  Weighing  and  measuring    .....       28 

Weighing;    A  pulverulent  sample;    Alloys;    Fluxes;    Weighing  the 

button ;  Measuring  of  fluxes    ........ 

Manner  of  charging  the  sample ;  The  mixing  scoops,  illustrated  . 

II.     CHEMICAL  OPERATIONS. 

Classification;  Working  by  the  dry  method;  Ignition,  carbonizing, 
calcining,  in  a  neutral  atmosphere,  with  exclusion  of  air,  with  ad- 
mission of  air,  with  reagents  for  decomposing  .  .  .  .31 

Roasting;   Roasting  dish  and  spatula,  illustrated  .         .         .         .32 


Vlll  CONTENTS. 

PAGE 

Modifications      ...........       33 

Fusion  ;  Oxidizing  fusion  ;  Reducing  fusion         .....       34 

Purifying  fusion  ;  Precipitating  fusion  ;  Mixing  fusion  ;  Remelting ; 
Liquating  fusion  (liquation)  ;  Sublimation  and  distillation ;  Opera- 
tions by  the  wet  method  ;  Assays  by  gravimetric  analysis  .  .  35 

Method  for  metallic  sulphides 36 

Evaporation  of  the  solution;  Precipitation  of  the  solution;  Kipp's  ap- 
paratus, illustrated  .         .         .         .         .         .         .         .         .37 

Debray's  apparatus,  illustrated ;  Filtration  ;  Filtering  apparatus  .       38 

Decantation ;  Drying  precipitates  ;  Igniting  precipitates       .          .          .39 
Blast-lamp,  illustrated ;  Desiccator,  illustrated ;   Assays  by  volumetric 

analysis  ;  The  final  reaction 40 

Operations;   Solution;  Preparation  of  the  standard  solution         .          .       41 
Measuring  andtitration  of  the  assay  liquid  ;  Stoppered  measuring  flasks, 

illustrated;  Pipettes,  illustrated 42 

Burettes,  illustrated  ;  Assays  by  colorimetric  analysis  *         .         .44 

III.     ASSAY  FURNACES. 

General  remarks ;  Muffle  furnaces        .         .         .         .         .         .         .45 

Furnaces  for  solid,  free  burning,  flaming  fuel       .....       46 

Plattner's  muffle  furnace  for  coal,  with  the  stoke  hole  in  front,  illus- 
trated .  47 

Muffle  furnace  with  the  stoke, hole  at  the  back,  illustrated;  Charcoal 

and  coke  furnaces;  Assay  furnaces  for  charcoal,  illustrated       .         .       49 
Gas  furnaces  (coal  gas)  ;  Perrot's  gas  muffle  furnace,  illustrated  .         .       50 
Draught  or  wind  furnaces    .          .         .          .         .         .          .          .         .51 

Placing  of  the  assay  vessels  in  the  furnace  ;  Firing  ;  Taking  the  vessels 
from  the  furnace     ..........       52 

Furnaces  used  in  the  Berlin  School  of  Mines,  illustrated      .         .         .53 
Wind  furnaces  for  free-burning  (flaming)  coal ;  Wind  furnaces  for  il- 
luminating gas ;  Perrot's  furnace,  illustrated    .         .         .         .         .55 

Wiessnegg's  gas  furnace  ;  Roessler's  furnace  for  the  production  of  high 

temperatures,  illustrated 56 

Fletcher's  direct  draft  crucible  furnace,  illustrated        .         .         .         .57 

Blast  furnaces    .         .         .         . 59 

Sefstrbm's  furnace,  illustrated  ;  Fletcher's  gas-injector  furnace,  illus- 
trated    ...  60 

Furnaces  for  sublimation  and  distillation  ;  A  sublimation  furnace,  illus- 
trated ;  A  distillation  furnace,  illustrated  .  .  .  .  .61 

Retorts,  illustrated 62 

Organic  combustion  furnaces 63 


CONTENTS. 


IV.     ASSAY  VESSELS. 

PAGE 

General  remarks  ;  Assay  vessels  for  the  dry  method  ;   Clay  vessels          .     G3 
The  principal  vessels,    etc.  ;  Vessels  without  feet  ;  Roasting  dishes  ; 
Scorification  or  calcining  vessels  ;  Refining  dishes  ;  Crucibles,  illus- 
trated      ............     64 

Graphite  crucibles  ;  Soapstone  crucibles  ;  Vessels  with  feet  ;  Crucibles 
for  lead  and  copper  smelting;    Other  clay  vessels;    Wrought-iron 
vessels  ;  Crucibles  for  assay  of  lead,  with  or  without  lip  .         .         .       65 
Vessels  of  bone  ash  ;  Cupels,  illustrated      ......       66 

Wait's  machine  for  making  cupels       .......       67 

Vessels  of  other  materials  ;  Assay  vessels  for  the  wet  method  ;  For 
assays  by  gravimetric  analysis  ;  Articles  of  glass  ;  Of  porcelain  ;  Of 
other  materials  ;  For  assays  by  volumetric  analysis  ;  For  assays  by 
colorimetric  analysis  .........  68 


V.    BALANCES  AND  WEIGHTS. 

Balances  ;  An  ore  balance  ;  Bullion  or  button  balance  ;  An  apothecary 
balance  ;  A  rough  scale  ;  Weights  ;  The  gramme  weight  ;  Centner  ; 
Austrian  and  English  assay  weights  .  .....  69 

American  assay  weights       .........       70 


VI.    TOOLS  AND  IMPLEMENTS. 

General  remarks  ;  Furnace  tools          .......       70 

Implements  ;  For  preparing  the  assay  sample  ;  Sampling  ;  For  drying 

the  samples  ;  For  comminuting  the  samples  ;  For  sifting  ;  For  wash- 

ing; For  weighing;  For  charging   ........       71 

Implements  for  transporting  the  assaying  vessels  and  for  manipulating 

the  same  in  the  furnace,  illustrated  .         .         .         .         .         .72 

Implements  required  for  the  reception  and  further  treatment  of  the 

assay  samples  after  they  have  been  taken  from  the  furnace         .         .       73 

VII.     ASSAY  REAGENTS. 

Reagents  for  dry  assays  ;  Reducing  agents  ;  Estimation  of  the  reducing 
power  ............  75 

Oxidizing  agents  ;  Quantities  of  litharge  required  for  the  decomposition 
of  the  various  metallic  sulphides  ;  Preparation  of  litharge  entirely 
free  from  silver  ........  .  .76 

Solvent  agents;  Acid;  Basic     ........       77 

Precipitating  or  desulphurizing  agents  ;  Sulphurizing  agents  ;  Concen- 
trating fluxes  ;  Preparation  of  pure  silver  .....  78 


X  CONTENTS. 

PAGE 

Decomposing  and  volatilizing  fluxes  ;  Air-excluding  fluxes  .         .       79 

Reagents  for  wet  assays ;  For  assays  by  gravimetric  and  colorimetric 
analysis;  Acids;  Bases  and  salts;  Metals  for  precipitation;  For 
volumetric  assavs  .  80 


SPECIAL  DIVISION. 
I.    LEAD. 

Lead  ores ;  Assays  of  lead  in  the  dry  way ;    Sulphurized  substances ; 

Galena,  etc.,  without  foreign  metallic  sulphides;  Precipitation  assay       81 
Rich  galena  (with  little  earths)  ;   Assay  in  an  iron  pot  (Belgian  assay)        82 
Assay  of  lead  matt  free  from  copper,  poorer  ores,  and  slag,  in  different 
countries         ...........       83 

Assay  with  potassium  cyanide  in  clay  crucibles 84 

Galena  with  more  earths  ;  Assay  with  black  flux  (potassium  carbonate 
and  flour)  and  metallic  iron,  in  clay  crucibles  .....  85 

Practice  in  different  countries 86 

Upper  Harz,  assay  with  potassium  carbonate ;  Charge         .         .         .87 
Galena  containing  large  quantities  of  Earths ;  Lead  monosulphide  with 

foreign  metallic  sulphides ;   Roasting  and  reducing  assay  .  *       .       88 

Practice  in  Hungary ;  Assay  with  sulphuric  acid  ....       89 

Oxidized  substances ;  Lead  oxides  free  from  earths  (litharge,  minium, 
skimmings  (Abstrich),  etc.)  ;  Lead  oxides  with  earths ;  Salts  of  lead 
oxide,  viz.,  lead  carbonate  (cerussite),  lead  chromate  (crocoisite), 
lead  phosphate  (pyromorphite),  mimetene  (lead  arsenate),  and  yellow 

lead  ore  (wulfenite) 90 

Lead  sulphate  (anglesite,  lead  fume,  dross,  sweepings,  tailings,  skim- 
mings, etc.);  Lead  silicate  (slags)  .......       91 

Alloys  of  lead ;  Wet  assays ;   Assay  by  gravimetric  analysis ;  Assays 
in  Bleiberg  in  Carinthia,  and  other  places         .....       92 

Mohr's  process  ;  Practice  of  various  assayers       .....       93 

Volumetric  processes ;  Colorimetric  processes  ;  Electrolytic  processes          94 

II.     COPPER. 

Ores ;  Native  copper 95 

Dry  assays          .         .         .         .      •  .         ."-..'        .         .         .         .96 


Dry  assays       •  i         .         .  •  .         ."-..' 

German  copper  assay ;  Ores  with  sulphur,  antimony,  or  arsenic ;  Roast- 
ing ;  Pyrites  ;  Reducing  and  solvent  fusion      .         . 


97 


CONTENTS.  xi 

PAGE 

Examples  of  charges ;  American  charge      ......       93 

Refining ;  Lead  ;  Refining  on  the  dish  with  borax       ....       99 

By  itself  without  borax  and  lead  (Hungarian  speiss  assays)  .  .  100 

Differences  allowed  in  assays ;  Refining  with  lead  and  borax  (Musen 

Assay) 101 

Refining  by  cupellation       .         .         .         .         .         .         .         .         .102 

Refining  with  the  blowpipe ;  Oxidized  substances  without  sulphur  .  103 
Alloys  of  copper;  Cornish  copper  assay;  Wet  assays;  Gravimetric 

assays 104 

Modified  Swedish  assay  .  .  .  .  .  .  .  .  .105 

Precipitation  with  iron 106 

Correction  for  iron  that  may  be  contained  in  the  precipitated  copper; 

Color  of  pure  precipitated  copper 107 

Precipitation  with  zinc  free  from  lead  and  arsenic  ;  Granulated  zinc  .  108 
Gravimetric  method  for  the  determination  of  copper  recommended  by 

Dr.  F.  A.  Genth 109 

Electrolytic  assays 110 

Use  of  Meidinger-Pinkus's  battery  and  Clamond's  thermo-electric 

battery;   Platinum  spiral  and  platinum  foil       .          .         .          .         .111 

Platinum  dish,  illustrated  and  described       .          .          .         .         .         .113 

Classen's  method  for  the  electrolytic  determination  of  metals,  illustrated 

and  described 114 

Copper  as  recently  precipitated  sulphide ;  Determination  of  the  copper 

in  the  form  of  cuprous  sulphide        .         .         .         .         .         .         .116 

Apparatus  for  igniting  in  a  current  of  hydrogen  .         .         .         .117 

Assay  with  sulpho-cyanide ;  Nickel  coins    .         .         .         .         .         .118 

Copper  alloyed  with  tin  (bronze)  ;  Volumetric  assays  .  .  .119 

Parkes's  assay  with  potassium  cyanide 120 

Steinbeck's  modified  method  of  assaying  copper;  Examination  of  cop- 
per precipitated  with  iron  or  zinc ;  Fleitmann's  method  with  ferric 

chloride 122 

Method  with  sodium  sulphide  in  an  ammoniacal  solution  ;  Method  with 

protochloride  of  tin  .  .  .  .  • 124 

Haen's  method  recommended  by  Fresenius;  Colorimetric  methods; 

Heine's  assay  for  poor  ores  and  products  (slags,  etc.)  .  .  .125 
Jaquelin-Hubert's  method  for  considerable  percentages  of  copper  .  126 
Determination  of  arsenic  in  copper ;  Determination  of  phosphorus  in 

copper    .         .         .         .         .         .         .         •         •         •         •         .127 

III.     SILVER. 

Principal  ores ;  Assays  for  non-alloys  .         .         .         .         ,         .128 

Wet  assays ;  Fire  assays ;'  Collecting  the  silver  with  lead ;  Scorification 
assay;  The  quantity  of  lead  to  be  used  .  .  .  .  .  .129 


Xll  CONTENTS. 

PAGE 

The  quantity  of  borax  ;  The  number  of  samples  to  be  taken        .         .     130 

Table  of  charges ;         ,     131 

Practice  in  Hungary  and  the  Lower  Harz   .          .         .     •     .         .         .133 

Crucible  assay    .         .         . ".         .134 

Charges  of  various  countries        .         .         .         .         .  •      ,  •      .  •      .135 

Other  charges  for  sweepings ;   Results  obtained  in  assaying  sweepings 
and  other  refuse,  recorded  by  Gorz  .         .         .         .'        .         .137 

Combined  lead  and  silver  assay ;  Litharge ;  Cupellation  of  the  argen- 
tiferous lead  (assaying  by  the  cupel  or  eupellation)  .  • "    .-      .     138 
Assay  of  native  silver  ores ;  Examination  of  lead  ores  for  traces  of  silver     141 
Wet  assays ;  Balling's  volumetric  assay       .         .         .         .       •  •         .     142 

Assays  of  alloys ;  Dry  assays  ;  Lead  bullion  ;   Silver  amalgam  ;  Copper 
poor  in  silver  .-       .          .         .          .         .         ....         .     143 

Cupriferous  silver  or  fine  silver  (coins,  refined  silver,  etc.)  .         *         .     144 
Correction  table  for  the  absorption  by  the  cupel,  determined  by  the 
French  Commission  on   Coinage  and  Medals ;   Results  obtained  in 
Freiberg;  Wet  assays     .          .         .         .        ";  -       .  -       .         »         .     147 

Volumetric  assays ;  Gay-Lussac's  method  with  sodium  chloride ;  Pre- 
paration of  the  assay  solution  ;  Flasks,  illustrated  and  described       .     148 
Gay-Lussac's  apparatus,  illustrated  and  described         .         ,         .         .150 
Calculation          .         .         .         .         .    .     .         .       .  .         .         .  151 

Preparation  of  the  normal  solution ;  Gay  Lussac's  Tables  for   deter- 
mining the  fineness  of  silver  alloys  .         .        >t         .         .         .     152 
Volhard's  assay  with  sulpho-cyanide  .         .         .  .         .155 

Cobalt  and  nickel ;  Mercury       '.      ...         ....-•       .'  ,    .         .156 

Determination  of  silver  and  copper  in  one  solution  ;  Assay  by  iodide  of 
potassium  and  starch        ,         .         .         »         .         .         .         .         .     157 

Gravimetric  analysis  ;  Determination  of  selenium  in  silver   .         .         .     158 
Electrolytic  determination  of  silver     .         .         .         .         .         .         .159 

Hydrostatic  assay       .         .         .         .  -,     .- 160 


IV.     GOLD. 

Gold  ores;  Non-alloys  ;  Mechanical  assay  by  washing  for  determining 
the  approximate  percentage  of  gold  in  earthy  and  gravelly  mine- 
rals poor  in  gold ;  Practice  in  Montana 161 

Practice  in  Australia  ;  Fire  or  fusion  assays  ;  Smelting  the  gold  with 
lead;  Scorification  assay  for  ores  of  every  kind  ;  Crucible  assay  .  162 

Substances  with  earths  and  oxides  (gold  quartz,  slag,  gold  sweepings) ; 
American  gold  ores ;  Rheinsand ;  Assay  with  nothing  but  red  lead 
(litharge)  as  flux  .  . 163 

Ores,  etc.,  with  combinations  of  sulphur,  antimony,  or  arsenic ;  Pyrites 
poor  in  gold 164 


CONTENTS.  xiii 

PAGE 

Tailings  containing  a  small  amount  of  auriferous  pyrites  ;  Hungarian 
smelting  works ;  Gold  ores  containing  tellurides  .  .165 

Cupellation  of  the  auriferous  lead ;  When  the  laminated  button  breaks 
up  ;  When  the  flattened  button  does  not  break  up  .  .  .  .166 

Wet  assay  (Plattner's  chlorination  process)  ;  Alloys  of  gold ;  Gold 
amalgam;  Auriferous  lead  and  bismuth  .  .  .  .  .  .167 

Auriferous  iron,  steel,  etc.  ;  Alloys  of  gold  and  silver,  with  or  without 
copper ;  Preliminary  test  for  alloys  free  from  copper ;  The  color  of 
the  alloy ....  168 

An  examination  of  the  touchstone ;  Preliminary  assay  of  cupriferous 
alloys  by  cupellation  ;  With  lead  alone  ;  The  quantity  of  lead  re- 
quired for  alloys  of  gold  with  silver  and  copper  .  .  .  169 

With  an  addition  of  lead  and  silver     .         .          .          .         .         .         .170 

Coins,  the  standard  of  which  is  known  ;  Preparation  of  chemically  pure 
gold;  Roberts' s  process  .  .  .  .  .  .  .  .171 

Roll  assay  for  argentiferous  gold ;  Preliminary  assay ;  Weighing  the 
assay  sample;  Charging;  Cupelling 172 

Flattening  (laminating)  the  button      .          .          .         .         .         .          .173 

Boiling  in  nitric  acid  .          .         .          .          .          .          .         .         .174 

Washing  (rinsing  off  the  rolls)    .          .          .          .          .  .         .175 

Drying  and  annealing  of  the  rolls  ;  Weighing  of  the  rolls ;  Loss  of  gold 
in  cupelling  .  .  .  .  .  .  .  .  .  .  .176 

Action  of  platinum,  rhodium,  and  iridium  .          .          .          .         .         .177 

D'Hennin's  process  for  separating  iridium;  Palladium;  To  obtain 
good  results  in  cupelling  gold 178 

Pulverulent  assay  (Strubprobe)  of  auriferous  silver      ....     180 

Different  modes  of  determining  the  gold  ;  Separation  of  auriferous  sil- 
ver grains  from  samples  of  ores  ;  Alloys  of  gold  with  copper ;  Quar- 
tation  of  gold  with  cadmium  .  .  .  .  ,  .  .  .181 

Advantages  offered  by  this  method  of  quartation ;  Juptner's  volumet- 
ric assay  of  gold  . 182 

Preparation  of  the  ferrous  ammonium  sulphate  solution  ;  Preparation 
of  the  permanganate  solution  ;  Separation  of  gold  from  platinum  by 
electrolysis 183 

Toughening  brittle  gold 184       , 

V.     PLATINUM. 

Ores;  Native  platinum       .         .         .         .         .         .         .         .         .184 

Assay  of  platiniferous  ores  ;  Fire  assays  ;  Percentage  of  sand  ;  Percent- 
age of  gold;  Percentage  of  platinum  ;  Wet  assay  ....  185 

Alloys  of  platinum  ;  Gold  with  platinum  ;   Silver  with  platinum  ;   Silver    . 
and  gold  with  platinum  .          .         .          .          .  .          .         .186 

Electrolytic  assay 187 


XIV  CONTENTS. 


VI.  NICKEL. 

PAGE 

Ores 187 

Fire  assay  (Plattner's  assay)  ;  Compounds  free  from  copper;  Com- 
pounds containing  metallic  sulphides ;  Arsenizing  ....  188 

Compounds  free  from  sulphur  and  rich  in  arsenic  ;  Reducing  and  sol- 
vent fusion  ;  Modifications  which  may  occur ;  Addition  of  iron  filings  189 

Arsenizing  and  fusion  in  one  operation  ;  Slagging  off  of  the  arsenical 
iron 190 

Modifications;  Dearsenizing  ;  Slagging  off  the  cobalt  arsenide ;  Cupri- 
ferous compounds  ;  Plattner's  method  .  .  .  .  <. .  .  191 

When  the  percentage  of  copper  is  small ;  Wet  method  partially  used 
when  the  percentage  of  copper  is  large  ;  The  processes  .  .  .  192 

Nickeliferous  pyrrhotine ;  Compounds  soluble  with  difficulty,  as,  for 
instance,,  slags  .  .  .  .  .  .  .  ."«'•'.  193 

Compounds  containing  antimony ;  Wet  assay  ;  Gravimetric  assay ; 
Electrolytic  assay .194 

Processes  when  iron  is  present  in  small  and  large  quantities         .         .     195 

Process  when  zinc  is  present        .         .         .         .         .         .          .         .197 

Determination  of  nickel  in  pyrites  and  matt;  assay  of  New  Caledonia 
ores  .  .  .  .  .  .  .  .  .  .  ]  98 

Electrolytic  determination  of  copper,  nickel,  and  cobalt  in  speiss         .     199 

Other  assays       .         . 200 

The  separation  of  nickel  and  cobalt ;  separation  of  the  iron  ;  Nickelifer- 
ous solution  from  the  assay  with  sulpho-cyanide  for  determining  cop- 
per in  nickel  coins  201 

Volumetric  assay  with  sodium  sulphide 202 

Separation  of  cobalt ;  Volumetric  assay  of  nickel  and  cobalt  according 
to  Donath 203 

Colorimetric  assay       ..........     204 

VII.  COBALT. 

Ores ;  Assays  of  cobalt ;  Object  of  the  assays ;  Determination  of  cobalt 
by  the  dry  or  wet  method ;  Determination  of  the  blue  coloring  pow- 
der (density),  and  the  beauty  of  the  colors  ;  Smalt  assay  .  .  204 

Assay  to  determine  the  quality  of  color;  assay  to  determine  the  inten- 
sity    .  .  .206 

VIII.     ZINC. 

Ores;  Dry  assays  ;  Assay  by  distillation     .         .         .         .         .         .207 

Indirect  assay 208 

Wet  assays  ;  Gravimetric  assays ;  Determination  of  zinc  as  zinc  sul- 
phide   209 


CONTENTS.  XV 

PAGE 

Determination  of  zinc  as  zinc  oxide ;  Electrolytic  assay        .         .         .     210 
When  copper  is  present;   Parodi  and  Mascazzini  on  precipitation  of 

zinc  from  its  sulphate  solution 211 

Zinc  assay  according  to  Rheinhardt  and  Ihle        .         .         .         .         .212 

Millot  on  the  electrolytic  determination  of  zinc  in  ores  ;   According  to 
Classen  .         .         .         .         .         .         .         .         .         .         .         .213 

Volumetric  assays  ;   ShafFner's  assay  with  sodium  sulphide    .         .         .214 

Indicators  for  recognizing  the  final  reaction 215 

Points  to  be  observed  ;  The  quantity  of  the  hydrated  ferric  oxide ; 
Shade  of  coloration  of  the  hydrated  ferric  oxide ;  The  quantity  of 

fluid;  Measuring  the  volume  of  liquid 216 

Removal  of  admixtures  having  a  disturbing  effect — copper,  manganese, 

lead,  etc 217 

Zinc  used  for  fixing  the  standard  solution ;  Arrangement  of  the  light ; 
Assay  with  potassium  ferrocyanide  .......     218 

Galetti  on  determining  zinc  with  potassium  ferrocyanide ;  Determina- 
tion of  zinc  by  decomposing  the  sulphide  of  zinc  with  chloride  of 
silver,  and  determining  the  zinc  from  the  equivalent  content  of  chlo- 
rine, according  to  Mann  219 

Preparation  of  the  titrating  solutions ;  Determination  of  zinc  from  its 
combinations  with  sulphur  by  decomposition  with  nitrate  of  silver, 

Balling's  method 220 

Determination  of  lead,  copper,  and  zinc  in  one  solution,  according  to 
this  method;  Schober's  volumetric  assay 221 


IX.     CADMIUM. 

Ores;  Electrolytic  assay ;  Processes  of  Clark  and  Tver       .         .         .     222 
Processes  of  Classen,  Beilstein,  and  Jawein        .         .         .         .         .223 


X.     TIN. 

Ores  ;  Determination  of  tinstone  by  washing ;  Saxon  assay  of  tin  ;  De- 
termination of  tin  by  washing  in  Cornwall 223 

Fire  assays ;  German  assay          ........     224 

Modifications  which  are  necessary — When  the  ore-  contains  many  earthy 
admixtures ;  When  the  ore  contains  foreign  metallic  sulphides,  arse- 
nides, and  antimonides 225 

Modification  necessary  on  account  of  the  ease  with  which  tin  oxide  is 
slagged  off';  When  separate  grains  of  tin  are  found  ;  When  tix  oxide 
is  combined  with  silicate  (as,  for  instance,  in  tin  ore  slags)        .         .     226 
Cornish  assay  of  tin  ;  Level's  assay  with  potassium  cyanide          .         .     227 
Wet  assays ;  Gravimetric  assays 228 


XVI  CONTENTS. 

PAGE 

Determination  of  tin  in  tin  slags 229 

Volumetric  assays ;  Determination  of  tin  by  means  of  iodine        .         .     230 
Determination  of  tin  by  means  of  potassium  permanganate           .         .231 
Determination  of  lead  in  tin  ;  Detection  of  tin  in  presence  of  antimony ; 
Electrolytic  determination  of  tin 232 


XI.     BISMUTH. 

Ores  .         .         .         . 233 

Fire  assays ;  Ores  and  compounds  free  from  sulphur  (native  bismuth ; 
tetradymite,  bismuthic  cupel  ash,  etc.)  ;  Sulphurized  bismuth  ores; 
Various  processes 234 

Wet  assays ;  Assay  of  ore ;  Separation  of  bismuth  from  lead ;  Accord- 
ing to  Patera  ..........  235 

Determination  of  the  percentage  of  lead  and  silver  ;  according  to  Ull- 
gren ;  Tin  oxide  ;  Lead  and  bismuth  ;  Electrolytic  assay  .  .  236 

XII.     MERCUHY. 

Ores  ,  •  .  •• 236 

Fire  assays;  Assays  yielding  free  mercury  ;  Different  processes    .         .237 

Combustion  furnace,  illustrated  and  described 238 

Assays  in  which  the  mercury*is  determined  in  combination  with  gold ; 

Eschka's  process      .         ...         .         .         .          .         .         .         .239 

Prevailing  working  assay  in  Idria  (Austria)  ;  Table  of  compensating 
differences  allowed  in  the  results :  Teuber's  process  for  testing  mer- 
cury  240 

Kiistel's  assay ;  Assay  of  cinnabar ;  Wet  assays ;  Gravimetric  assay ; 
Volumetric  assays   ..........     241 

Electrolytic  determination  of  mercury ;  Processes  of  Classen,  Smith, 
and  Knerr  242 


XIII.     ANTIMONY. 

Ores  ;  Fire  assays  ;  Liquation  process  for  determining  antimonium  cru- 
dum  ;  Determination  of  antimony  in  antimony  sulphide ;   Assay  by 
precipitation   ...........     243 

Roasting  and  reducing  assay        .........     244 

Wet  assays;  Gravimetric  assay  ;  Becker's  method       ....     245 

Volumetric  method  ;  Weil's  method  of  determining  antimony  with  pro- 

tochloride  of  tin .     246 

Table  of  cubic  centimeters  of  protochloride  of  tin  solution  used  for 
every  25  cubic  centimeters  of  assay  solution  (2  grammes=250  cubic 
centimeters)  correspond  to  per  cent,  of  antimony  .  .  .  .  248 


CONTENTS.  XV11 

PAGE 

Determination  of  the  simultaneous  presence  of  iron,  copper,  and  anti- 
mony; Volumetric  estimation  of  antimony  in  the  presence  of  tin; 
Electrolytic  determination  of  antimony ;  Processes  of  Parodi,  Mas- 
cazzini,  Luckow,  and  Classen  .  .  .  .  .  .  .249 

XIV.  ARSENIC. 

Ores ;  Fire  assays  ;  Native  arsenic  ;   Arsenious  acid     ....  251 

Realgar  (red  orpiment)  ;  Assays  for  the  determination  of  realgar ;   As- 
says for  the  determination  of  yellow  orpiment ;  Wet  assay ;  Gravi- 
metric assays  ..........  252 

Wet  method  combined  with  the  dry    .......  253 

Volumetric  assays;  T.  Mohr's  estimation  of  arsenious  acid;  Pearce's 

method  of  determining  arsenic         .......  254 

Canby's  modification  with  oxide  of  zinc       ......  255 

Arsenic  in  glass  ..........  255 

XV.  URANIUM. 

Ores  ;  Wet  assays  ;  Gravimetric  assays  ;  More  accurate  analytical  pro- 
cess    255 

Patera's  technical  test ;   Alibegoff's  process      « 256 

Volumetric  assay  ;   Zimmermann's  process  .....  257 

Method  of  determining  uranium  with  potassium  dichromate  and  iodine 

(Zimmermann's  process)          ........  258 

XVI.     TUNGSTEN. 

Wolfram 258 

Fire  assay  ;  Wet  assays  ;  Gravimetric  assays;  Sheele's  method  ;  Berze- 

lius's  method;  Margueritte's  method        ...                            .  259 
Cabenzl's  method  ;  separation  of  tungsten  from  tin  ;  Talbott's  method  260 
Volumetric  assay  ;   Zettner's  method  ;  Preparation  of  the  titrating  solu- 
tion           261 

XVII.     CHROMIUM. 

Ores;  Wet  assays .261 

Gravimetric- assays;  Direct  assay ;  Pourcel's  method  .  .         .     262 

Best  methods  for  decomposing  chrome  iron  ores  ;  Hager's  method ; 
Fels's  method ;  F.  Clarke's  method ;  Indirect  assay ;  Volumetric 

assay •     263 

B 


XV111  CONTENTS. 


XVIII.     MANGANESE. 

PAGE 

Ores ;  Assays  of  pyrolusite          ........     264 

Gravimetric  assays      .  -    .         .          .         .          .          .          .          .266 

Method  of  Fresenius-Will,  illustrated 267 

Method  of  Fikentscher-Nolte      ...  .268 

Volumetric  assays       .         .          .          .         .          .          •  •         .269 

Bunsen's  method  with  iodine;   Apparatus    .  .  .     270 

Level's  method  with  iron    .          .          .          .          .          .          .          .         .272 

Volhard's  method       .          .          . 273 

Execution  of  the  assay  ;  Determining  the  strength  of  the  perman- 
ganate ;  Hampe's  method        .         .          .          .         .          .          .          .274 

Belani's  method  ;  Electrolytic  assays 275 

XIX.     SULPHUR. 

Ores 276 

Assays  by  distillation  for  the  determination  of  the  amount  of  sulphur 
which  an  ore  may  yield  ;  Sulphur  earths ;  Gerlach's  •  method  ;  Iron 
pyrites ;  Assays  of  sulphur  for  the  determination  of  the  quantity  of 
sulphur  contained  in  a  substance  ;  Dry  assay  (raw-matt  assay)  .  277 

Hungarian  assay 278 

Wet  assays  ;  Gravimetric  assays  ;  Gravimetric  determination  of  sulphur 
in  pyrites  according  to  Lunge  .......     279 

Fresenius's  observations  ;  Deutocom's  method  ;  Bodewig's  method      .     280 
Determination  of  sulphur  in  pyrites  waste ;   Working  test  for  deter- 
mining the  residue  of  sulphur  in  the  roasting  charge          .          .    '      .281 
Volumetric  assays ;   Wildenstein's  assay       ......     282 

Volumetric  determination  of  sulphur  in  ores  which  contain  either  sul- 
phur alone  or  also  sulphates 283 

Estimation  of  sulphur  in  metallic  lead 284 

XX.     FUELS. 

Assays  of  fuels ;  Determination  of  the  amount  of  hydroscopic  water ; 

Yield  of  carbon 285 

Determination  of  the  coking  quality  of  coal  according  to  Richter ;  Vola- 
tile products ;  Determination  of  the  ash  .  .  .  .  .  286 

Amount  of  ash  in  different  kinds  of  fuel ;  Determining  the  amount  of 
sulphur  in  a  coal  or  its  ash  ;  Determination  of  heating  power  .  .287 

Berthier's  method  of  determining  the  absolute  heating  power;  Welter's 
law 288 

Determination  of  the  sulphur 290 


CONTENTS.  xix 

PAGE 


Physical    and    chemical    behavior;    Examination    of    furnace   gases; 

Orsat's  apparatus,  illustrated  and  described      .          .         .         .          .291 
Bunte's  burette,  illustrated  and  described    .         .         .         .         .         .     294 


APPENDIX. 

Tabular  synopses ;   Atomic  weights     .         .         .         .         .         .         .297 

Fusing  points  of  metals  and  furnace  products  ;  Glowing  temperatures  .  298 
Plattner's  method ;  Erhard  and  Schertel's  experiments  on  the  fusing 

points  of  metals,  alloys,  furnace  products,  rocks,  and  silicates  .  .299 

Erhard  and  Schertel's  tables 300 

Table  of  furnace  products  and  gangues  ;  Lower  Harz  working  assays  ; 

lead 301 

Copper ;  Iron  ;  Zinc 302 

Silver;  Gold;  Sulphur;  Schaffner's  assay  of  zinc  as  modified  by 

Brunnlechner          ..........     303 

Experiments  on  a  heat  regulator  at  the  United  States  Assay  Office, 

New  York  ;  Automatic  heat  regulator,  illustrated  and  described  .  307 

Dry  assay  of  iron  ores 310 

Proportion  of  fluxes   .          .         .         .          .          .          .          .         .         .312 

Fluxes  best  adapted  for  ores  or  metallurgical  products  .  .  .313 

Fluxes ;  Silica ;  Glass ;  China  clay  ;  Lime ;  Assay  in  large  unlined 

crucibles          .         .          .          .         .          .          .          .          .          .          .314 

Reducing  agent ;  Results 315 

THE  MKTRIC  SYSTEM  OF  WEIGHTS  AND  MEASURES. 

The  metric  system      .          .          .          .         .          .          .         .'.         .317 

Weights  and  measures;  Apothecaries'  weight,  U.  S.  ;  Avoirdupois 
weight;  Relative  value  of  troy  and  avoirdupois  weights;  Wine 
measure,  U.  S.  ;  Imperial  measure,  adopted  by  all  the  British  col- 
leges;  Relative  value  of  apothecaries'  and  imperial  measures  .  .319 
Relative  value  of  weights  and  measures  in  distilled  water  at  60°  Fahr.  ; 
Value  of  apothecaries'  weight  in  apothecaries'  measure ;  Value  of 
apothecaries'  measure  in  apothecaries'  weight ;  Value  of  avoirdu- 
pois weight  in  apothecaries'  measure  ;  Value  of  apothecaries'  meas- 
ure in  avoirdupois  weight ;  Value  of  imperial  measure  in  apothe- 
caries' and  avoirdupois  weights 320 


XX  CONTENTS. 

TABLES  SHOWING  THE  RELATIVE  VALUES  OF  FRENCH  AND  ENGLISH 

WEIGHTS  AND  MEASURES. 

PAGE 
Measures  of  length     .         .         .         .         .         .         .         .         .         .321 

Superficial  measures ;  Measures  of  capacity 322 

American  measures  ;  British  imperial  measures  ;   Weights   .          .          .     323 
Different  values  for  the  gramme  ;  Avoirdupois  ;  Troy  (precious  metals)  ; 

Apothecaries'  (pharmacy)  ;  Carat  weight  for  diamonds    .          .          .     324 
Proposed  symbols  for  abbreviations     .          .         .          .          .         .          .325 

Ready-made  calculations     .         . 32G 

HYDROMETERS  AND  THERMOMETERS. 

Hydrometer  (areometer)     .........     329 

Thermometers    .          .         .          .         .         .          .         .         .          .          .331 

Centigrade  and  Fahrenheit 332 

Comparison  of  Centigrade  and  Fahrenheit  scales  and  approximate 
steam  pressure  in  pounds  and  atmospheres  per  square  inch  due  to 
the  temperature  ..........  334 

INDEX       .         .         .         .         .         .         .  335 


UNIVERSITY 


ASSAYING 


GENERAL  DIVISION. 


1.    OBJECT  OF  THE  ART  OF  ASSAYING.1 

THE  art  of  assaying  (doeimacy,  from  $oxi[ia%siv,  to  test)  is  a 
branch  of  analytical  chemistry.  Its  object  is  the  quantitative 
determination,  in  the  shortest  possible  time,  of  the  products  of 
mining  and  metallurgical  operations,  as  well  as  the  quantitative 
examination  of  many  natural  and  artificial  products  derived  from 
other  sources,  such  as  coins,  fuels,  etc.  Formerly,  in  order  to 
reach  the  result  with  the  greatest  expedition,  the  dry  method 
(dry  assay)  was  chosen  for  producing  the  chemical  reaction ;  but, 
as  this  was  frequently  done  at  the  expense  of  accuracy  in  the 
result  of  the  assay,  the  wet  method  (wet  assay,  gravimetric  analysis, 
analysis  by  measure  or  volumetric  analysis,  and  colorimetnc  analy- 
sis) is  also  used  in  modern  times.  But  it  has  by  no  means  entirely 
displaced  the  dry  method,  for  the  latter  is  employed  in  all  cases 
where  results  sufficiently  accurate  are  more  quickly  reached,  or 
where  suitable,  simple  wet  assay  methods  (as  in  assaying  lead, 
cobalt,  nickel,  gold,  and  silver)  cannot  be  substituted  for  it. 

Sometimes  a  combination  of  both  is  employed  (assays  of  lead, 
icold,  etc.).  Recently  the  method  of  precipitating  metals  by 
electrolysis  has  been  employed  to  great  advantage. 

1  Kerl,   Eisenprobirkunst,    Leipzig,   1875.      Balling,   Probirknnde,   Braun- 
schweig,   1879.       Mitchell,    Manual   of    Practical   Assaying,    London,    1888. 
Ricketts,  Notes  on  Assaying  and  Assay  Schemes,  New  York,  1887. 

2  B.  u.  h.  Ztg.,  1869,  p.  181  (Luckow) ;  1875,  p.  155;  1877,  p.  5  (Schweder). 
(4rothe.  polyt.  Ztschr.,  1877,  p.  11  (Bertrand).    Quantitative  Chemical  Analy- 
sis by  Electrolysis  (Classen),  Trans.,  New  York,  1887. 

2 


1 8  ASSAYING. 

Volumetric  assays  can  mostly  be  performed  in  a  shorter  time, 
which  is  an  important  item  where  much  assaying  has  to  be  done. 
The  results  they  yield  are  either  very  accurate,  or  at  least  suffi- 
ciently exact1  for  metallurgico-technical  purposes ;  they  are  less 
expensive,  but  require  greater  experience  and  more  chemical 
knowledge  on  the  part  of  the  operator,  and  special  apparatus  of 
accurate  construction.  While  by  the  dry  method  the  metal 
assayed,  or  one  of  its  alloys  having  a  known  composition,  is 
weighed  directly,  in  volumetric  assays  it  is  calculated  from 
certain  reactions  of  the  reagents  employed,  and  the  result  may 
possibly  be  vitiated  on  account  of  the  presence  of  foreign  sub- 
stances, of  whose  presence  there  is  not  always  an  indication. 

Colorimetric  assays  are  chiefly  employed  for  determining  very 
small  quantities  of  metals  which  either  could  not  be  detected  by 
other  methods,  or,  if  so,  then  only  by  very  tedious  processes 
(copper,  lead) ;  but  recently  they  have  been  developed  so  as  to 
adapt  them  for  substances  rich  in  metal  (copper). 

The  bloivpipe  is  frequently  used  for  a  preliminary  assay.2 

I,  Mechanical  Manipulations, 

2.  SAMPLING. 

It  is  absolutely  necessary  that  the  small  quantity  of  sample 
with  which  the  assay  is  made  should  represent  the  average  com- 
position of  the  ore-heap,  etc.,  from  which  it  is  taken.  The  man- 
ner of  taking  samples  varies  according  to  the  character  of  the 
substances  to  be  assayed,  viz  : — 

A.  Non-alloys  (ores,  matt,  speiss,  slag,  etc.). 

1.  Substances  in  fragments,  either  homogeneous  or  heterogene- 
ous in  composition. 

1  B.  u.  h.  Ztg.,  1869,  p.  330.     (Compare  gravimetric  and  volumetric  assays 
of  Cu,  Fe,  Zn,  Sb.) 

2  Berzelius,  Anwendung  des  Lothrohrs,  Niirnberg,  1828.      Scherer,  Loth- 
rohrbuch,    Braunschweig,   1857.      Birnbaum,  Loth  rob  rbuch,   Braunschweig, 
1872.      Simmler,   Lothrohrchemie,   Zurich,  1873.      Hirschwald,  Lothrohrta- 
bellen,    Leipzig,   1875.       Landauer,    Lothrohranalyse,    Braunschweig,    187(j. 
Kerl,  Lothrohrprobirkunst,  Clausthal,  1877.     Landauer,  systematischer  Gang 
der  Lothrohranalyse,  Wiesbaden,  1878.      Plattner-Richter,  Probirkunst  mil 
dem  Lothrohr,  4  Aufl.,  Leipzig,  1878. 


SAMPLING.  19 

a.  Homogeneous  fragments,  many  iron  ores,  lead  and  copper 
ores,  etc. 

a.  Samples  from  the  heap.1 — Pieces  are  taken  at  random  (it  is 
best  to  do  so  with  bandaged  eyes)  with  the  hand  or  a  shovel, 
from  different  places  on  the  circumference  of  the  heap,  and  also 
from  the  interior,  after  the  tipper  layer  which  has  been  dried  by 
the  atmosphere  has  been  removed.     The  collected  lumps  (about 
100  kilogrammes,  220.54  Ibs. ;  in  Freiberg,  for  certain  ores,  one- 
tenth  of  the  heap)  are  comminuted  to  pieces  of  the  size  of  a  bean, 
either  by  means  of  rollers  or  stamps,  or  with  a  sledge-hammer. 
A  square  or  conical  heap  is  then  formed  of  the  pieces,  and  this 
is  divided  into  four  parts.      One  of  these  is  taken,  the  pieces 
forming  it  are  still  further  comminuted,  and  then  again  formed 
into  a  heap,  which  is  divided  as  before.     The  comminution  and 
reduction  are  repeated  several  times,  finally  upon  an  iron  plate 
provided  with  a  rim  (reducing-board),  until  at  last  from  J  to  1 
kilogramme  (1  to  2  Ibs.)  of  the  sample  remains,  in  such  commi- 
nuted form  that  it  will  pass  through  a  sieve  having  30  by  30 
meshes  to  the  square  centimeter  (about  75  meshes  to  the  square 
inch). 

(3.  Samples  taken  while  the  ore,  etc.,  is  being  weighed. — Pieces 
are  taken  at  random  from  every  lot  weighed,  and  the  collected 
pieces  comminuted  and  reduced  according  to  paragraph  a  (Upper 
Harz  copper  pyrites). 

/.  Samples  by  rasping. — Fuels,  etc.,  which  cannot  be  pulverized 
are  comminuted  by  a  rasp,  and  a  reduced  sample  made  from  this. 

$.  Slag  samples. — A  piece  of  slag  is  taken  every  time  the  slag 
is  tapped  or  run  off,  or  a  piece  is  broken  off  from  every  cone 
formed.  The  pieces  of  one  charge  are  comminuted  and  reduced 
in  the  manner  above  stated. 

b.  Heterogeneous  fragments. — (Gold  and  silver  ores,  many  cop- 
per ores,  coal  with  slate  and  pyrites,  etc.) 

a.  Sampling  by  the  cross  method.2 — When  the  grains  are  too 
dissimilar  and  too  coarse,  the  entire  heap  is  broken  up.  The 
broken  fragments  (as  large  as  a  walnut  for  less  valuable  ores, 
and  about  the  size  of  a  hazelnut  or  bean  for  the  more  valuable) 

1  B.  u.  h.  Ztg.,  1868,  p.  26  ;  ]872,  p.  59. 

2  Preuss.  Ztschr.  xvii.  137  (Mansfeld) ;  xviii.  223,  224  (Swansea). 


20  ASSAYING. 

are  passed  through  screens  or  cylindrical  sieves.  An  oblong  or 
square  heap,  30  to  40  centimeters  high,  is  then  formed.  Ditches 
about  20  to  30  centimeters  wide,  and  crossing  each  other,  are 
dug  out  with  a  shovel,  and  the  samples  are  then  taken  by  dig- 
ging them  out  from  the  top  down  to  the  bottom  of  the  squares, 
which  remain  standing  between  the  ditches.  These  samples  are 
comminuted  to  the  size  of  millet-seed,  thoroughly  mixed,  and 
formed  into  a  new  rectangular  heap,  which  is  again  crossed,  and 
samples  taken  from  it  in  the  manner  stated.  This  operation  is 
repeated,  finally  by  using  the  spoon,  until  the  samples  are  reduced 
to  a  powder.  (Method  in  the  great  ore  markets  of  Swansea  and 
Liverpool,  for  American  silver  ores  in  the  Upper  Harz  and  in 
Freiberg,  etc.) 

f^.  Sampling  by  dropping  the  ore.1  (Sturzprobe.) — The  ore  is 
dropped  through  a  funnel  standing  over  a  pyramid  of  sheet-iron, 
which  is  divided  into  four  divisions  by  partitions  projecting  over 
the  edge,  into  which  the  ore  is  distributed.  The  ore  from  one 
of  the  divisions  is  comminuted  and  dropped  through  a  funnel 
into  a  similar  but  smaller  pyramid.  This  operation  is  repeated, 
smaller  pyramids  being  used  every  time,  until  a  sufficiently 
reduced  sample  has  been  obtained  (method  in  Chili  and  Colorado). 

2.  Small  ore  and  pulverized  substances. 

a.  Sampling  while  weighing. — The  small  ore  must  be  carefully 
mixed,  and,  in  case  it  should  be  rich,  it  is  best  to  have  it  in  such 
a  condition  that  not  over  15  per  cent,  of  coarse  material  will 
remain  behind  in  passing  it  through  a  sieve  having  10  meshes  to 
the  square  centimeter  (25  meshes  to  the  square  inch),  but,  other- 
wise, it  may  be  coarser.  It  is  generally  weighed  in  quantities  of 
50  to  100  kilogrammes.  Three  spoonfuls  are  taken  from  dif- 
ferent places  of  every  lot  weighed,  and  placed  in  wooden  troughs 
standing  near  the  scale.  All  the  samples  taken  from  one  lot  are 
mixed  together  and  a  heap  is  formed  from  them.  This  is  reduced 
by  quartering,  or  by  the  crossing  method.2 

Samples   of   goldsmiths'   sweepings  (scrapings,  fragments   of 

1  Preuss.  Ztschr.  xxiv.  49.  B.  u.  h.  Ztg.  1872,  p.  232  (Chili).  Ann.  d. 
Mines,  1878,  XIII.  606  (Colorado). 

8  Kerl,  Oberliarzer,  Hiittenprocesse,  1860,  p.  195. 


SAMPLING.  21 

crucibles,  rags,  etc.)  are  taken  by  incinerating  the  entire  mass  in 
order  to  destroy  organic  matter.  The  mass  is  then  comminuted 
by  stamping  or  trituration,  and  passing  it  through  a  sieve  having 
meshes  the  size  of  a  grain  of  sand  (less  than  1  millimeter,  0.039 
inch).  The  iron  in  the  coarse  mass  remaining  in  the  sieve  is 
extracted  by  using  a  mUgnet,  and  the  residue  fused  with  soda  and 
borax,  cast  into  a  bar,  weighed,  and  sampled  by  chipping  from 
top  and  bottom.  The  portion  that  has  passed  through  the  sieve, 
freed  from  iron  with  the  magnet,  is  then  weighed,  sampled  from 
every  weighing,  then  united,  quartered,  and  triturated  until  every- 
thing passes  through  a  very  fine  sieve.  It  is  then  assayed,  and 
the  yield  of  metal  obtained  from  both  coarse  and  fine  material  is 
calculated. 

b.  Sampling  before  weighing. — This  is  done  by  passing  with  a 
hollow  sheet-iron  cylinder  in  several  places  through  the  heap 
down  to  the  bottom.  The  lower  end  of  the  cylinder  is  provided 
with  a  valve  which  when  closed  retains  the  charge,  and  with  a 
handle.  The  samples  are  then  mixed  and  reduced  as  above 
described  (Freiberg). 

In  some  of  the  German  smelting  works,  the  ore,1  when  it  is 
bought,  is  sampled  by  weighing — 
to  within  10  Ibs.  when  it  contains  up  to  0.5  per  cent.  Ag,  or 

0.01  per  cent.  Au. 
"         1  Ib.  when  it  contains  over  0.5  to  5  per  cent.  Ag,  or 

0.0105  to  0.1  per  cent.  Au. 
0.1  Ib.  when  it  contains  over  5  to  50  per  cent.  Ag,  or 

0.1005  to  1  per  cent.  Au. 
"         0.02  Ib.  if  it  contains  more. 

10  Ibs.  if  the  ores  contain  no  gold  or  silver. 

3.  Substances  in  a  state  of  fusion. — An  average  sample  may  be 

obtained  in  the  following  manner :  A  dry  tapping-bar,  previously 

heated,  is  held  in  the  fluid  mass  (slag,  etc.).     When  the  bar  has 

become  cold,  the  adhering  mass  is  broken  off,  comminuted,  and 

1  Bezahlungstarife  fur  den  Einkauf  von  freraden  Erzen  u.  Gekratzen  auf 
den  fiscalischen  Hiittenwerken  bei  Freiberg.  Clausthal,  1870.  Oestr.  Ztschr. 
1869,  No.  44.  Engl.  Standard  f.  Zinnerze,  B.  u.  h.  Ztg.  1862,  p.  261 ;  f.  Kup- 
fererze,  1862,  p.  316.  Spanische  Tarife,  B.  u.  h.  Ztg.  1868,  p.  26.  Tarno- 
witzer  Erztaxe  in  Preuss.  Ztschr.  xiv.  217. 


22  ASSAYING. 

then  mixed  and  reduced.  In  this  operation,  however,  the  iron 
must  not  decompose  the  fused  material  (a  possible  separation  of 
lead  may  occur,  for  example,  from  lead  matt  and  lead  speiss). 

B.  Alloys. — These  are  homogeneous  when  in  a  fluid  state, 
especially  after  they  have  been  stirred.  But  when  solidified, 
they  show  a  different  composition  in  different  places  (edge,  cen- 
tre, top,  bottom).1  In  sampling,  this  must  be  taken  into  con- 
sideration. 

1.  Sampling  by  cutting. — The  sample  (2.5  grammes  from  every 
ingot  of  silver,  1.5  grammes  from  those  of  gold)  is  cut  from  the 
upper  and  lower  sides  on  opposite  ends  of  the  ingot  by  means 
of  a  hollow  chisel  and  hammer.  (In  England  and  the  United 
States,  the  opposite  edges  are  chipped  off.)  The  samples  are 
hammered  or  rolled  out,  the  resulting  sheets  cut  into  shreds,  and 
each  sample  is  assayed  by  itself  (0.5  to  1  gramme  of  each  is 
weighed  off  for  the  purpose).  The  yield  is  calculated,  and  either 
the  average  is  given  (gold  assays),  or  the  lowest  yield  (sometimes 
in  silver  assays).  This  method  is  best  adapted  for  alloys  of 
tolerably  uniform  composition,  but  is  also  employed  for  those 
showing  a  considerable  difference  in  the  lower  and  upper  sam- 
pling. 

For  instance,  the  lower  sample  from  refined  Upper  Harz  silver 
is  from  y^o  ^°  ToVfr  ricner  than  the  upper,  the  percentage  of 
gold  increasing  towards  the  bottom.  The  centre,  as  a  rule,  con- 
tains more  silver  than  the  edge.  In  the  "five-mark  piece"  the 
centre  is  y^Vfr  richer  than  the  edge,  and  the  same  is  the  case  with 
the  "thaler"  as  they  are  stamped  from  a  bar  poorer  on  the  edge 
than  in  the  centre.  For  this  reason,  when  taking  samples  from 
such  coins,  it  is  best  to  cut  out  a  quadrant,  cut  off  the  corners, 
and  assay  them.  In  this  way  the  assay  samples  represent  the 
composition  of  both  periphery  and  centre  of  the  bar  from  which 
the  coins  have  been  stamped.  Fewer  differences  occur  in  gold 
than  in  silver  coins. 


1  Kerl,  Grundr.  d.  allgemeinen  Huttenkunde,  2  Aufl.,  1879,  p.  15.  Dingier, 
cciii.  106 ;  ccxv.  431.  Ber.  d.  deutsch.  chem.  Ges.  1874,  p.  1548,  B.  u.  h. 
Ztg.  1874,  p.  63 ;  1875,  p.  251. 


SAMPLING.  23 

2.  Sampling  by  boring.1 — This  is  done  by  boring  through  the 
edge  and  centre  of  the  ingot.    By  this  means  a  sample  is  obtained 
from  the  centre  of  the  ingot,  which  is  not  the  case  in  chipping  a 
sample,  but  the  ingot  is  made  unsightly.     It  is  very  difficult  to 
mix  the   borings  uniformly,  and  it  is  therefore  better  to  fuse 
them  under  a  covering  of  charcoal  powder.     It  is  best  to  use  a 
mechanical  contrivance  for  boring  through  thick  pieces.     This 
consists  of  a  lever  weighted  at  one  end,  and  a  drill,  operated  by 
the  hand  in  the  centre. 

3.  Sampling  by  dipping. — This  is  obtained  in  the  same  manner 
as  mentioned  on  p.  21,  for  instance,  from  refined  copper.    Another 
method  of  taking  samples  is,  by  dipping  the  curved,  bright  end 
of  a  pair  of  pincers,  or  of  an   iron  rod,  into  the  metal  bath. 
When  the  pincers  or  iron  rod  has  become  cold,  the  crust  adher- 
ing to  the  end  is  broken  oif.     A  sample  is  generally  taken  from 
the  surface  of  silver  while  it  is  being  refined,  and  one  from  the 
under  side  of  the  congealed  refined  silver. 

4.  Sampling  by  granulation. — This   sample   indicates  in  the 
most  reliable  manner  the  average  value  of  the  metal.      It  is 
obtained  in  the  following  manner :   the  bars  of  precious  alloys 
are  smelted  in  a  black-lead  crucible.     The  mass,  while  in  fusion, 
is  stirred  with  a  rod  of  iron  or  clay,  and  a  sample  is  scooped  up 
with  a  small  ladle  from  the  bottom  of  the  crucible.     It  is  then 
poured  in  a  thin  stream  into  a  copper  vessel  filled  with  warm 
water,  to  which  a  gentle  rotary  motion  is  given  by  means  of  a 
broom ;  or  the  sample  is  directly  poured  through  a  birch  broom. 
The  resulting  granulated  metal  is  then  carefully  dried.     Alloys 
of  base  metal  (as  granulated  lead2)  are  fused  under  coal-dust  and 
then  directly  poured  upon  an  iron  plate. 

The  following  samples  are  taken  for  producing  coins :  ingot 
sample  from  the  metals  to  be  alloyed ;  granulated  or  crucible 
sample  from  the  fused  alloys ;  stock  sample  from  sectors  of  the 
finished  coins;  and  a  sample  from  defective  coins  which  have 
been  thrown  out  and  fused  together,  for  instance  inside  of  four 
weeks. 

1  Mitchell,  Prac.  Assaying,  1888,  p.  364. 

2  B.  u.  h.  Ztg.,  1869,  p.  278  (Brixlegg). 


24  ASSAYING. 

3.    PREPARATION  OF  THE  SAMPLE. 

Alloys  are  prepared  by  rolling  out  and  cutting  up  the  resulting 
sheets ;  or  the  granulated  metal  is  used  without  further  prepara- 
tion. The  following  operations  may  be  required  for  non-alloys : — 
1.  Determination  of  moisture. — The  sample  is  divided,  by 
weighing  with  reduced  weights,  into  as  many  centners  or  kilo- 
grammes or  pounds  as  are  actually  contained  in  the  lot  (for 
instance,  in  Freiberg,  1  centner  weight  =  75  grammes).  The 
weighed  portion  is  heated  in  an  iron  or  copper  pan  or  directly 
in  the  removable  scale-pan  of  the  balance,  by  holding  it  over  a 
heated  stove  or  a  brazier  of  charcoal,  and  constantly  stirring  it 
until  a  cold  plate  of  glass  or  slate,  when  held  over  it,  shows  no 
deposition  of  moisture,  and  two  successive  weighings  agree.  The 
heating  should  be  carefully  conducted,  so  that,  with  sulphur 
compounds  for  example,  no  odor  of  sulphurous  acid  shall  be 
developed,  and,  with  organic  substances,  no  carbonization  shall 
take  place  (this  may  be  guarded  against  by  holding  a  piece  of 
paper  in  the  mass).  Water-baths  are  used  for  drying  the  sample 
at  100°  C.  (212°  F.).  These  are  copper 
Fig.  1.  boxes,  with  double  walls,  the  intermediate 

space  (Fig.  1)  containing  water;  or,  they 
consist  of  hemispherical  copper  or  enamelled 
iron  vessels,  placed  one  within  the  other, 
leaving  an  intermediate  space  for  water ;  or 
of  two  cylinders,  one  placed  within  the  other 
(Scheibler's1  steam  apparatus).  Where  a  de- 
terminate temperature,  high  or  moderate,  is  required,  it  is  best 
to  use  Fresenius's  drying  disk  of  cast  iron,  which  is  heated  from 
below  (Fig.  2).  It  is  25  centimeters  in  diameter,  and  4  centi- 
meters thick ;  b  is  the  handle,  36  centimeters  high ;  c  are  small 
brass  dishes  with  numbered  handles  fitting  into  suitable  recesses  ; 
d,  a  case  filled  with  copper-filings  for  the  reception  of  the  ther- 
mometer e.  Besides  these,  air-baths?  commonly  called  thermo- 
stats, are  also  used. 

1  Dingier,  ccxxiii.  312.     Muspratt's  Cheraie,  v.  1635. 

2  Bunsen's  Luftbad  mit  Temperaturregulator  in  Kerl's  Grundr.  der  Eisen- 
probirkunst,  1875,  p.  3.     Rauliu's  Warmeregulator  in  Dingier,  ccxxvii.  263. 


PREPARATION  OF  THE  SAMPLE. 


25 


2.  Pulverizing  the  desiccated,  mass. — This  should  be  done  care- 
fully, to  avoid  loss  of  dust,  either  in  a  covered  mortar,  or  on  a 


Fig.  2. 


flat  disk  of  cast  iron  as  is  shown  in  Fig.  3.      The  iron  plate 
should  be  perfectly  true  and  have  a  smooth  surface.     The  rub- 


Fig.  3. 


bers  are  made  of  iron  and  weigh  from  15  to  60  pounds  (6.8  to 
27.2  kilogrammes). 

3.  Sifting. — Brass  wire  sieves  are  generally  used  in  preference 
to  hair  sieves.  For  less  valuable  ores  the  sieves  have  from  14 
to  20  meshes  to  the  square  centimeter  (about  35-50  to  the  square 
inch),  and  more  valuable  ores  from  28  to  32  meshes  to  the  square 


26 


ASSAYING. 


centimeter  (from  70-80  to  the  square  inch).  Brittle  substances 
will  pass  through  the  sieves  without  difficulty,  but  those  with 
malleable  admixtures  will  leave  a  flattened  residue  in  the  sieve ; 
as,  for  example,  ores  carrying  native  silver  and  copper,  silver 
glance,  granules  of  lead  in  slag  and  thin  matt,  sweepings  con- 
taining gold  and  silver  (p.  20),  etc.  In  case  hard  gangue  (quartz) 
is  to  be  sifted,  the  fine  mass  which  has  passed  through  the  sieve 
is  several  times  rubbed  together  with  the  coarse  residue  remain- 
ing upon  the  sieve,  until  everything  has  passed  through  it.  The 
residue  of  soft  gangue  is  weighed  and  at  once  assayed  by  itself, 
and  the  fine  siftings  separately  also,  after  they  have  been  mixed 
upon  glazed  paper  and  passed  several  times  through  a  coarse 
sieve.  The  entire  yield  is  then  calculated  by  adding  the  product 

Fig.  4. 


of  both  together.  The  material  ready  for  assaying  is  packed  in 
wooden  boxes,  glass  bottles,  or  small  linen  bags.  Dishes  of 
ordinary  potter's  clay  (Mehlscherben)  may  serve  for  the  reception 
of  the  stamped  ore  and  lots  of  samples  while  they  are  weighed 


PREPARATION  OF  THE  SAMPLE. 


27 


out  for  assaying;  they  have  an  outer  diameter  of  from  80  to  100 
millimeters  on  the  bottom,  100  to  200  millimeters  on  the  top, 
and  are  from  40  to  45  millimeters  high  (Hungary). 

4.  Washing. — This  is  done  to  separate  specifically  heavier  sub- 
stances from  lighter  ones  (roasted  tin  ore,  gold  gravel,  etc.),  or  to 
obtain  a  uniform  grain  (smalt  assays).  The  mass,  comminuted 
as  fine  as  possible,  is  placed  in  a  beaker-glass  and  water  poured 
upon  it.  It  is  then  thoroughly  stirred  up,  when  it  is  allowed  to 
settle,  and  the  turbid  liquid  poured  off;  or  it  is  washed  in 
Schulze's  washing  apparatus  (Fig.  4)  by  allowing  water  to  flow 


Depth  at  a=3/S 
Depth 


Thickness  Of  Skwel  Re- 


on AB 


from  a  Mariotte's  bottle,  A,  through  d,  upon  the  mass  contained 
in  the  glass  1 ;  the  different  sizes  of  grain  will  settle  in  the 
glasses  2  and  3,  the  finest  grains  in  the  beaker-glass  B.  Another 
mode  of  washing  the  substances  is  by  using  an  iron  vanning 
shovel  (Fig.  5).  The  washed  mass  should  be  occasionally  ex- 
amined with  a  magnifying  glass  or  blowpipe  as  to  its  physical 


28  ASSAYING. 

characteristics  (for  instance,  silver  ore  for  the  presence  of  metallic 
sulphides,  antimony  and  arsenic  in  order  to  regulate  the  addition 
of  lead  before  smelting). 

The  art  of  vanning  is  apt  to  be  one  of  the  most  useful  accom- 
plishments to  an  assayer  or  miner.  It  is,  however,  somewhat  diffi- 
cult to  learn,  and  requires  considerable  practice  before  reliable 
results  can  be  obtained.  Perhaps  the  best  way  to  learn  vanning  is 
to  thoroughly  mix  known  quantities  of  finely  powdered  tin  ore  and 
sand  together,  and  see,  by  repeated  trials,  how  nearly  they  can  be 
separated.  Thus,  for  example,  thoroughly  mix  20  grains  (1.30 
grammes)  of  tin  ore  with  500  grains  (32.4  grammes)  of  finely 
powdered  sand.  Place  on  shovel  or  trough  with  just  sufficient 
water  to  cover  the  mixture,  and  as  the  sand  is  separated  out  from 
time  to  time,  wash  it  in  a  dish.  When,  as  far  as  possible,  all  the 
sand  has  been  separated  out,  dry  the  residue  (tin  ore)  remaining 
on  the  shovel  and  weigh.  The  sand  which  was  washed  out  into 
the  dish  is  then  taken  and  revanned  in  the  same  manner  in  order 
to  separate  out  any  tin  ore  yet  remaining;  dry,  weigh,  and  add 
to  weight  first  determined. 

4.    WEIGHING  AND  MEASURING. 

Before  every  weighing,  the  balance  must  be  tested  as  to  its 
equilibrium.  The  substance  to  be  weighed  should  be  cold,  and 
must  not  be  placed  directly  upon  the  scale-pan,  but  upon  suitable 
smaller  pans,  watch-glasses,  etc.;  hygroscopic  substances  in  closed 
tubes.  The  balance  beam  should  be  raised  from  the  knife  edge 
every  time  before  a  weight  is  put  into  or  removed  from  the  pan. 
The  weights  must  not  be  put  in  the  pan  at  random,  but  system- 
atically, as  this  is  the  only  way  of  saving  time.  The  highest  prob- 
able weight  should  be  added  first,  then  the  next  lowest,  and  so 
on  until  the  equilibrium  has  been  established.  The  pans  should 
then  be  changed  in  order  to  test  the  correctness  of  the  weight. 
Perfect  equilibrium  of  the  balance  is,  however,  not  absolutely  es- 
sential, as  a  correct  weighing  may  be  obtained  by  placing  the 
substance  to  be  weighed  in  one  pan,  and  in  the  other  pan  any 
convenient  material  as  a  make-weight,  such  as  tinfoil,  shot,  gran- 


WEIGHING  AND   MEASURING.  29 

ules  of  lead,  etc.,  until  equilibrium  is  established.  The  balance 
is  then  raised,  the  weighed  substance  is  removed  from  the  pan, 
and  sufficient  weights  to  counterpoise  the  balance  are  put  in  its 
place.  The  sum  of  these  will  give  the  correct  weight  of  the 
sample. 

1.  Weighing:  a.  A  pulverulent  sample. — The  dried  sample  is 
poured  upon  glazed  paper  and  spread  out  in  spirals  with  the 
spatula.    It  is  then  drawn  together  towards  the  centre  by  radial 
bands.     Some  of  it  is  now  taken  with  the  spatula  from  the  bot- 
tom to  the  top  of  the  heap,  the  weights  are  placed  upon  the  left 
pan  of  the  balance,  and  the  sample  is  continuously  poured  into  a 
counterpoised  saucer  or  watch-glass  placed  upon  the  other  pan, 
by  gently  tapping  on  the  handle  of  the  spoon,  until  equilibrium 
has  been  established.     In  case  too  much   has   been  poured  in, 
some  of  it  is  removed,  but  the  balance,  while  this  is  done,  must 
be  arrested.     Large  quantities  are  weighed  upon  a  watch-crystal 
counterpoised    by  granules  of  lead  or  shot.     Hygroscopic  sub- 
stances are  conveniently  weighed  by  filling  a  stoppered  glass  tube, 
12  to  14  centimeters  long,  and  8  to  10  millimeters  wide,  with 
them,  noting  the  weight,  and,  after  pouring  out  the  requisite 
amount   of   sample,  again   weighing    the   tube;    the   difference 
between  the  two  weighings  will  give  the  weight  of  the  quantity 
abstracted. 

6.  Alloys. — They  are  converted  either  into  granulated  form  or 
into  small  strips  or  splinters.  These  are  collected  in  a  glass  or 
copper  saucer  and  placed  by  means  of  the  forceps  in  the  right 
pan  of  the  balance  while  the  weights  are  placed  in  the  left. 

c.  Fluxes. — In  weighing  these,  very  great  accuracy  is  not  of 
so  much  importance.  They  are  placed  either  directly  upon  the 
pan  of  the  balance,  provided  it  is  not  attacked  by  them,  or  other- 
wise upon  a  tared  watch-crystal. 

2.  Weighing  the  button. — The  button  is  taken  hold  of  with  the 
forceps  and  placed  upon  the  left  pan  of  the  balance,  and  the 
weights  are  then  put  upon  the  right ;  but,  as  has  been  stated,  the 
balance  must  always  be  arrested  before  the  weights  are  put  on  or 
removed. 

3.  Measuring  of  fluxes. — Granulated  lead  (test  lead)  free  from 
silver  is  measured  with  large,  gauged,  iron  spoons  numbered  on 


30  ASSAYING. 

the  handles,  or  with  a  glass-tube,  one  end  of  which  is  closed  with 
a  stopper,  while  in  the  other  is  a  wooden  cylinder  provided  witli 
a  scale. 

5.    MANNER  OF  CHARGING  THE  SAMPLE. 

The  sample  is  poured  either  directly  into  the  crucible  without 
any  fluxes  (as  in  roasting),  or  the  fluxes  are  added  in  such  a 
manner  that — 

1.  The  sample  lies  on  the  bottom  of  the  crucible,  and  the 
fluxes  are  placed  upon  it  in  consecutive  order  without  stirring 
the  mass  up.     When  this  is  done,  the  mass  will  not  puff  up  as 
easily  when  it  is  heated  (charges  with  carbonaceous  mixtures,  for 
instance,  assay  of  lead  with  carbonate  of  potassa,  flour  and  iron). 

2.  The  sample  is  added  to  the  fluxes  already  in  the  crucible, 
in  cases  where  the  puffing  up  of  the  charge  on  heating  is  not 
feared,  and  is  intimately  mixed  together  (for  instance,  assay  of 
lead  with  potassium  carbonate). 

3.  The  sample  is  mixed  with  the  fluxes  before  it  is  placed  in 
the  crucible.     The  mixing  is  done  in  a  mixing-scoop  of  copper 
(Fig.  6)  by  means  of  a  spatula.     The  scoop  is  about  140  milli- 
meters long  and  40  millimeters  wide. 

Fig.  6. 


The  mixture  is  poured  into  the  crucible  through  the  spout 
of  the  scoop,  about  20  millimeters  wide,  a  brush  being  used  to 
brush  out  the  last  traces  of  the  mixture;  or,  in  case  a  very 
vigorous  chemical  reaction  is  desired,  the  sample  and  fluxes  are 
first  intimately  rubbed  together  in  a  mortar  of  stone  (porcelain, 
serpentine,  agate),  or  of  metal  (steel,  cast-iron,  brass).  Open 
mixing-scoops  of  copper  provided  with  a  handle  (Fig.  7)  are 
used  for  mixing  the  charge,  or  for  receiving,  in  consecutive  order, 

1  [Care  should  be  taken  that  they  are  bright  and  smooth. — Gr.] 


WORKING  BY  THE  DRY  METHOD. 

the  substances  constituting  it,  or  for  pouring  them  into  the  glow- 
ing crucible  standing  in  the  heated  furnace  (assays  of  lead,  Eng- 
lish assay  of  copper). 


II,  Chemical  Operations, 

6.    CLASSIFICATION. 

These  operations  are  divided  into  those  by  the  dry  and  those 
by  the  wet  method,  and  are  either  preliminary  (roasting,  etc.),  or 
capital  operations  (smelting,  etc.). 

7.  WORKING  BY  THE  DRY  METHOD. 

These  operations  are  carried  on,  either  below  the  fusing  point 
(ignition,  carbonizing,  calcining,  roasting),  with  or  without  admit- 
tance of  air ;  or  at  a  fusing  heat  (smelting) ;  or  volatile  substances 
are  to  be  expelled  by  heat,  and  their  vapors  condensed  to  the 
liquid  state  (distillation),  or  to  the  solid  state  (sublimation). 

1.  Ignition,  carbonizing,  calcining.1 — Heating  without  fusing — 

a.  In  a  neutral  atmosphere,  to  drive  out  volatile  substances  (for 
instance,  water  and  carbonic  acid  from  iron  ores),  or  to  change 
their  molecular  condition  (for  instance,  annealing  gold  and  silver 
alloys  before  rolling  them  out,  etc.). 

b.  With  exclusion  of  air  in  covered  pots  or  crucibles,  to  decom- 
pose metallic  sulphides  and  arsenides  (iron  and  arsenical  pyrites 
in  the  dry  assay  of  blende),  to  effect  reduction  (ignition  of  tin 
ore  with  charcoal),  or  to  arsenize  or  dearsenize  the  substances 
(assay  of  nickel  and  cobalt). 

c.  With  admission  of  air  in  roasting  dishes  (determination  of 
ash  in  fuel,  combustion  of  bitumen  in  copper  schist  and  black- 
band  iron  ore,  oxidation  of  cement  copper,  etc.). 

d.  With  reagents  for  decomposing  substances  insoluble  in  acids 
(for  instance,  silicates  with  four  times  their  weight  of  a  mixture 

1  Gaslampen  in  Dingier,  ccxxiv.  617;  ecxxv.  83  (Miincke).  Fresenius's 
Ztschr.  1879,  p.  257  (Ebell).  Bunsenbrenner  von  Glas  in  Dingier,  ccxxvii. 
85,  398. 


32  ASSAYING. 

of  13  parts  of  potassium  carbonate  and  10  parts  of  anhydrous 
sodium  carbonate  in  a  platinum  crucible). 

2.  Roasting. — Metallic  sulphides,  arsenides,  and  antimonides 
are  heated  in  presence  of  air  to  a  temperature  insufficient  for 
fusion,  but  which  permits  of  their  oxidation ;  metallic  oxides 
are,  therefore,  produced,  while  sulphurous,  arsenious,  and  (some- 
times) antimonious  acids  are  volatilized. 

The  process  is  as  follows  :  The  powdered  sample  is  spread  out 
in  a  shallow,  smooth  roasting  dish.  This  is  about  50  to  52 
millimeters  wide  in  the  clear,  and  8  to  10  millimeters  deep,  made 
of  not  too  refractory  clay,  and  has  rather  thin  sides.  It  is  lined 
with  reddle,  chalk,  or  oxide  of  iron,  and,  if  necessary,  in  order 
j,,.  o  to  increase  the  surface,  the  lined  sides  are 

marked  with  a  spatula  in  such  a  manner 
that  radial  furrows,  running  from  the  cen- 
tre towards  the  edges,  are  formed.  It  is 
then  placed  in  the  muffle  of  a  muffle-furnace  (Fig.  27)  and  heated 
at  a  gradually  increasing  temperature  until  it  glows  ;  the  heating 
must  be  the  more  gradual  the  more  fusible  the  sample.  (Anti- 
monial  and  arsenical  metals  are  more  easily  fused  than  metallic 
sulphides,  antimony  glance,  lead  sulphate,  and  "fahlerz"  contain- 
ing mercury).  The  mouth  of  the  muffle  is  left  open,  with  the 
exception  of  a  low  layer  of  pieces  of  wood  charcoal  touching 
each  other,  and  continued  in  a  forward  direction.  These  pieces 
in  a  glowing  state  heat  the  oxidizing  air  current.  The  roasting 
dish  must  occasionally  be  turned  around  during  the  operation. 
It  is  taken  from  the  muffle  when  the  mass  has  ceased  to  burn, 
and  oxidation  is  complete.  This  is  indicated  by  the  heated  mass 
ceasing  to  fume  and  no  longer  emitting  odors  of  sulphurous  or 
arsenious  acid,  and  the  metallic  lustre  having  been  replaced  by 
an  earthy  appearance.  If  this  should  not  be  the  case,  the  roast- 
ing dish  must  be  placed  back  into  the  muffle  until  these  signs 
make  their  appearance.  The  now  roasted  sample  may  be  some- 
what sintered  together.  It  is  then  rubbed  with  the  iron  knob,  6, 
of  a  wooden-handled  spatula,  after  being  loosened  from  the 
edges  of  the  roasting  dish  with  the  knife's  edge,  a,  of  the  rod. 
This  tool  (Fig.  9)  is  about  195  millimeters  long,  and  consists 


WOKKING  BY  THE  DEY  METHOD.  33 

of  the  iron  head  6,  about  16  millimeters  diameter,  and  the 
steel  knife-blade  «,  set  in  a  wooden  handle.  The  roasting  is 
repeated  once  or  several  times,  but  the  mass  must  be 
rubbed  up  previous  to  each  roasting.  It  is  then  mixed  ^ig'  9* 
with  1  or  2  volumes  of  powdered  wood  charcoal,  or  20 
to  25  per  cent,  of  graphite,  and  the  roasting  dish  with  its 
contents  is  again  placed  in  the  muffle  and  brought  to  a 
glow.  By  this  process  the  sulphates,  antimoniates,  and 
arseniates  formed  during  the  oxidizing  period  are  reduced 
to  metallic  sulphides,  antimonides,  and  arsenides,  while 
the  volatile  products  of  oxidation  escape  (reducing  roast- 
ing). These  compounds  when  all  the  carbon  has  been  consumed 
(which  may  be  readily  recognized  by  the  manner  of  glowing) 
will  be  again  converted  into  oxides ;  sulphurous,  arsenious,  and 
antimonious  acids  being  evolved  in  the  operation.  But  new  sul- 
phates, antimoniates,  and  arseniates  will  constantly  be  formed, 
and  these,  if  the  sample  is  to  be  roasted  as  completely  as  possible 
(for  instance,  copper  ores,  but  lead  ores  in  a  less  degree),  can  only 
be  removed  by  repeating  the  rubbing  up  of  the  assay  sample 
twice  or  three  times,  mixing  it  with  charcoal  powder,  and  glow- 
ing until  the  coal  is  completely  consumed,  although  even  after  this 
small  quantities  of  sulphates  will  nevertheless  remain.  When 
the  roasted  sample  has  become  sufficiently  cold,  it  is  placed  in 
an  iron  mortar  and  mixed  with  20  to  50  per  cent,  of  ammonium 
carbonate.  A  small  conical  heap  of  the  mixture  is  formed  in  the 
roasting  dish ;  this  is  covered  with  an  empty  roasting  dish  and 
quickly  ignited  until  the  odor  of  ammonia  can  no  longer  be 
detected.  When  this  is  the  case,  the  last  traces  of  sulphuric  acid 
in  the  roasted  sample  will  have  been  volatilized  in  the  form  of 
ammonium  sulphate.  (Lead  and  bismuth  sulphates  are  only 
incompletely  decomposed  by  ammonium  carbonate.)  The  roast- 
ing dish  is  now  taken  from  the  muffle  and  allowed  to  cool  off. 
The  sample  is  then  placed  in  a  mortar  and  rubbed  up. 

Modifications. — When  the  ores  are  refractory  (for  instance, 
copper  pyrites),  powered  charcoal  or  graphite  is  added  to  the 
sample  before  roasting,  in  order  to  shorten  the  time  required  for 
the  operation.  Very  fusible  substances  which  evolve  vapors 
(such  as  "fahlerz"  containing  mercury)  must  be  heated  very 
3 


34  ASSAYING. 

gradually.  To  diminish  the  loss  of  metal  (for  instance,  of  silver 
and  gold)  the  temperature  must  not  be  raised  higher  than  is 
absolutely  necessary.  The  loss  from  this  cause  is  greatest  with 
ores  containing  antimony,  arsenic,  zinc,  etc. 

3.  Fusion. — The  sample  is  brought  into  a  liquid  state,  either 
by  itself,  or  with  fluxes.  During  this  process  the  resulting 
products  (metal  button  or  regulus,  speiss,  matt,  slags)  arrange 
themselves  in  layers  according  to  their  specific  gravities,  and  are 
separated  from  each  other,  either  by  breaking  to  pieces  the  clay 
assay-vessels  in  which  they  have  been  fused,  after  they  have 
become  cold,  or  they  are  poured  out  while  still  in  a  fluid  state, 
into  iron  or  bronze  moulds,  where  the  separation  then  takes 
place.  Sometimes  the  fluid,  oxidized  substances  are  absorbed  by 
the  porous  sides  of  the  assay-vessel,  leaving  the  metal  button 
behind  (cupellation  of  lead  refining  copper  on  the  cupel).  The 
following  distinctions  are  made  according  to  the  object  of  the 
fusion  : — 

a.  Oxidizing  fusion. — In  this  process  the  following  may  serve 
as  oxidizing  agents :   the  oxygen  of  the  air,    demanding  open 
vessels  for  the  operation  (cupels,  calcining  and  roasting  dishes), 
which  must  be  heated  in  the  muffle-furnace  (for  instance,  cupel- 
lation of  lead,  refining  copper,  assay  of  cobalt  and  nickel);  or 
fluxes  yielding  oxygen,  and  then  open  or  covered  assay-vessels 
(pots,  crucibles),  and  muffle,  wind,  and  blast  furnaces  may  be 
used  (saltpetre  in  the  Cornish  assay  of  copper  and  in  the  assay  of 
chromium,  lead  oxide  in  the  assays  of  fuel,  silver  and  gold);  or 
both  at  the  same  time  (refining  of  black  copper).     The  resulting 
oxides  are  more  frequently  slagged  oif  by  themselves  or  by  sol- 
vent agents  added  as  a  flux  (borax,  glass,  etc.),  than  absorbed  by 
the  porous  vessel  used  for  fusing  (cupels). 

b.  Reducing  fusion. — This   operation   is  seldom  executed   by 
itself  with  reducing   agents  (coal,    flour,  colophony,   potassium 
cyanide),  but  generally  in  connection  with  fluxes  (potassium  or 
sodium  carbonate),  in  order  to  allow  of  a  better  collection  of  the 
particles  of  metal  (as  from  litharge,  white-lead  ore);  or  in  con- 
nection with  reducing,  fluxing,  and  solvent  agents  (borax,  glass, 
phosphorus  salt).     A  definite  low  temperature  must  then  be  used 
to  reduce  one  metallic  oxide,  while  the  metallic  oxides  with  more 


OPERATIONS  BY  THE  WET  METHOD.  35 

difficulty  reducible,  are  slagged  off  with  the  earths  which  may  be 
present  (assays  of  lead,  copper,  and  tin  ores).  Muffle,  wind,  and 
blast  furnaces  are  used.  The  vessels  used  for  this  process  (cruci- 
bles, pots)  should  be  roomy,  as  the  mass  puffs  up.  This  is  caused 
by  the  formation  of  carbonic  oxide  which  ignites  above  the 
vessels.  This  phenomenon  is  called  "flaming"  the  end  of  the 
operation  being  generally  indicated  by  its  cessation. 

c.  Purifyiitg  fusion. — This  is  more  frequently  used  in  connec- 
tion with  oxidizing  fusion  (p.  34)  and  reducing  fusion  (p.  34) 
than  by  itself  (assay  of  smalt,  assay  of   thin  matt). 

d.  Precipitating  fusi'on. — By  this  process  metallic  sulphides  (in 
assays  of  lead,  bismuth,  and  antimony)  or  arsenical  metals  (in 
the  assay  of  lead  ores  and  nickel  and  cobalt  ores  containing  bis- 
muth)  are   decomposed   by   iron.     The   desulphuration   of  the 
metals  is  promoted  by  suitable  fluxes  (potassium  or  sodium  car- 
bonate,  black   flux),  or   the  slagging  off  of  earthy  and   other 
admixtures  is  effected  (borax,  glass,  alkalies). 

e.  Mixing  fusion ,  to  prepare  alloys  by  fusing  different  metals 
together  (gold  and  silver  in  quartation). 

/.  Remdtingy  in  order  to  produce  the  sample  in  another  form 
(as,  for  instance,  by  granulation,  p.  23). 

g.  Liquating  fusion  (liquation\ — Liquation  of  easily  fusible 
substances  from  more  refractory  substances  (assay  of  antimony 
glance). 

4.  Sublimation  and  distillation. — The  sample  is  placed,  either 
by  itself  or  with  fluxes,  in  crucibles,  tubes,  or  retorts,  and  heated 
until  the  substances  volatilize,  and  the  vapors  are  then  condensed 
as  sublimates  (flaky  arsenic,  flowers  of  sulphur,  realgar),  or  as 
distillates  (mercury,  zinc)  in  suitable  condensers. 

8.    OPERATIONS  BY  THE  WET  METHOD. 

These  may  be — 

1.  Assays  by  gravimetric  analysis.1 

a.  The  sample  is  dissolved  in  acids,  in  a  porcelain  dish  cov- 

1  Rammelsberg,  quant.  Analyse,  Berlin,  1863.  Wohler,  Mineralanalyse, 
Gottingen,  1861.  Sonnenschein,  quant.  Analyse,  Berlin,  1864.  Rose-Fink- 
ener,  Mineralchemie,  Leipzig,  1865.  Fresenius's  quant.  Analyse,  6  Aufl.  1871. 


36 


ASSAYING. 


Fig.  10. 


ered  with  a  watch-crystal.  Or  a  bellied  flask  is  used  for  the 
purpose  (Fig.  10).  This  either  stands  upright  and  is  provided 
with  a  funnel,  or  is  placed  in  a  slanting  position  to 
prevent  the  liquid,  in  case  it  effervesces,  from  being 
thrown  out  of  the  mouth  of  the  flask.  The  vessel 
may  be  heated  on  a  sand-bath,  or  upon  a  wire 
gauze  over  a  lamp,  until  the  solution  is  complete,  or 
a  residue  showing  no  trace  of  ore,  etc.,  remains. 

The  following  method  is  used  for  metallic  sul- 
phides, which,  when  they  are  dissolved  with  acids, 
separate  sulphur  which  incloses  some  of  the  ore.  The  solution 
is  evaporated  to  dryness  in  a  porcelain  evaporating  dish.  The 
dry  mass  is  heated  over  a  lamp  until  the  sulphur  is  burned.  The 


Fig.  11. 


Fisr.  12. 


residue  is  digested  with  a  small  quantity  of  acid,  water  is  added 
to  this,  and  the  fluid  then  partly  filtered ;  but  in  doing  this  great 
care  must  be  observed.  The  residue  is  again  treated  with  acid, 

Classen,  quant.  Analyse,  Stuttgart,  1857.  Mensclmtkm,  Analyt.  Chemie, 
Leipzig,  1878.  Bolley,  techn.-chem.  Unters.,  Leipzig,  1879.  Muspratt's 
tech.  Chemie,  3  Aufl. 


OPERATIONS   BY   THE   WET   METHOD. 


37 


evaporated  to  dry  ness,  the  sulphur  burned,  etc.  If  it  is  necessary 
to  exclude  the  air,  the  apparatus  in  Fig.  11  is  used.  It  consists 
of  a  flask,  a,  with  a  rubber  cork,  6,  and  provided  with  a  rubber 
tube,  c  dj  having  a  slit  at/  and  closed  at  e  by  a  small  glass  rod. 

b.  Evaporation  of  the  solution  in  a  glass  flask  (Swedish  assay 
of  copper,  assay  of  lead  sulphate),  or  in  a  covered  porcelain  dish 
by  heating  it  in  the  sand-bath,  over  a  lamp,  or  on  the  water- 
bath. 

c.  Precipitation  of  the  filtered  or  unfiltered  solution  ;  or  where 
a  mass  evaporated  to  dryness  is  to  be  treated,  it  is  moistened 
with  a  little  acid,  allowed  to  stand  for  a  few  minutes,  and  then 
boiled  with  the  addition  of  a  small  quantity  of  water.     It  is  then 
filtered,  etc. 

Kipp's  apparatus  (Fig.  12)  is  well  adapted  for  precipitation 
with  sulphuretted  hydrogen. 

C,  a  glass  bulb,  receives  the  diluted  sulphuric  acid  from  the 
funnel  tube  e;  the  acid  enteres  the  glass  bulb  A  through  the 
tube  6.  It  rises  in  this  and  comes  in  contact  with  ferrous  sul- 

Fig.  13. 


phide  or  calcium  mono-sulphide  contained  in  the  bulb  B,  and 
the  gas  generated  escapes  by  the  tubulure  c  through  the  lateral 
tube  controlled  by  the  cock  d;  the  tubulure  c  also  serves  for 
filling  the  bulb  with  ferrous  sulphide ;  a  is  the  tubulure  for 
emptying  A. 


38  ASSAYING. 

Debray's  apparatus  (Fig.  13)  is  arranged  in  the  following 
manner  :  A  is  the  vessel  for  the  diluted  sulphuric  acid,  provided 
with  a  safety  tube  and  a  rubber  tube  a.  B  is  a  vessel  containing 
a  layer  of  glass  splinters,  piled  up  so  high  that  the  ferrous  sul- 
phide, lying  upon  it,  is  above  the  opening  o.  d  is  a  glass  tube 
provided  with  a  clip  (compression  stop-clock)  e;  C  is  a  wash- 
bottle,  /  the  pipe  for  conducting  away  the  gas.  By  opening  the 
cock  e  the  acid  flows  from  A  into  B,  and  sulphuretted  hydrogen 
is  disengaged.  By  closing  the  cock  the  fluid  is  forced  back  from 
B  to  A  ;  the  pressure  of  the  gas  may  be  increased  by  placing  A 
higher  up.  Instead  of  sulphuretted  hydrogen,  sodium  hypo- 
sulphite may  be  used  as  a  precipitating  agent. 

d.  Filtration. — A  funnel,  the  sides  of  which  have  a  slope  of 
60°,  is  generally  used  for  this  process ;  a  filter  of  paper  is  folded 
into  it,  and,  if  necessary,  covered  with  a  watch-glass.  If  the 
filtration  is  to  be  done  quickly,  the  filter  is  connected  with  an 
air-pump,1  or  compressed  air  is  used.2  Fig.  14  shows  a  filtering 
apparatus  connected  at  a  with  a  water  air-pump.  The  mouth  of 
the  flask  is  furnished  with  a  rubber  stopper  perforated  for  the 

Fig.  14.  Fig.  15. 


reception  of  the  funnel.  The  dotted  lines  below  this  represent  a 
perforated  test-tube,  through  which  the  liquid  is  drawn  into  the 
flask.  The  precipitate  on  the  filter  is  washed3  by  means  of  a 
wash-bottle  (Fig.  15). 

1  Fresenius,  quant.  Analyse,  1871,  p.  97.      Fresenius's  Ztschr.  f.  analyt. 
Chem.  ii.  359 ;  iv.  46  ;  1875,  p.  308. 

2  Fresenius's  Ztschr.  xvi.  92.     Dingier,  ccxxv.  81,  105. 

3  Buusen's  Auswaschen  der  Niederschlage  in  Fresenius's  Ztschr.  viii.  174. 


OPERATIONS    BY   THE   WET   METHOD. 


39 


Fig.  16. 


e.   Decantation. — When  a  precipitate  thoroughly  settles,  the 
clear  supernatant  liquid  may  be  poured  off.     The  precipitate  is 
then  repeatedly  washed  with  water  and  decanted.     To 
dry  the  precipitate,  the  contents  of  the  flask  (a  glass 
vessel  (Fig.  16)  with  straight  sides),  are  washed  into  a 
crucible  or  evaporating  dish,  with  as  little  wash-water 
as  possible  (precipitated  copper  and  gold,  tin  stone  puri- 
fied by  boiling  with  acid) ;  or  the  precipitate  is  filtered 
off,  and,  if  necessary,  also  the  sediment  remaining,  after 
the  water  used  for  decanting  has  been  poured  off. 

/.  Drying  precipitates.1 — The  filter,2  without  being  taken  from 
the  funnel,  is  covered  with  paper,  to  protect  it  against  dust,  etc., 
and  dried  in  an  air-bath,  or  a  water-bath.  Or,  it  is  removed 
from  the  funnel,  folded  up  and  dried  first  between  blotting  paper, 
and  then  in  a  covered  roasting-dish,  in  the  muffle-furnace  (assay 
of  lead  with  sulphuric  acid). 

g.  Igniting  precipitates? — If  the  substance  is  not  to  be  weighed 
upon  the  dried  filter,  it  is  highly  heated  with  the  filter  in  the 
roasting-dish  after  the  lid  has  been  removed.  Or,  the  precipitate 
is  carefully  detached  from  the  filter;  the  latter  is  folded  up, 

Fig.  17. 


wrapped  around  with  platinum  wire,  and  is  then  burned  over  a 
flame  or  directly  upon  the  cover  of  a  platinum  crucible,  or  in  a 

1  Mtirrle,  of  Pforzheim,  furnishes  distilling  apparatus  and  sand-bath  very 
suitably  combined,  with  steam  and  air  drying  closets  (these  are  in  use  in  the 
Berlin  School  of   Mines).       Bestimmuug  der   Niederschlage  ohne   Filtriren, 
Auswaschen  und  Trocknen  in  Fresenius's  Ztschr.  1877,  157;  1879,  p.  14. 

2  Filtrirpapiere  in  Fresenius's  Ztschr.  xvi.  59  ;  xviii.  246,  260. 

3  Fresenius's  Ztschr.  1875,  p.  328. 


40  ASSAYING. 

roasting  dish.  The  residue,  together  with  the  ashes  of  the  filter, 
is  placed  on  a  roasting  dish  and  ignited  in  a  muffle- furnace,  or 
in  a  platinum  and  porcelain  crucible  over  a  Bunsen  burner,  an 
ordinary  spirit-lamp  (Fig.  17),  or  a  blast-lamp. 

The  best  form  of  blast-lamp  is  shown  in  Fig*.  18;  it  consists 
substantially  of  a  Bunsen  burner  with  a  blast  attachment.  The 
blast  flame,  when  confined  by  the  loose  cap,  B,  is  compact  and 
extremely  powerful  owing  to  the  fact  that  the  air  mixture  is  par- 
tially made  before  the  blast  begins  to  act.  The  taps  A  and  C, 
respectively,  admit  the  gas  and  air. 

If  necessary  the  crucible  is  allowed  to  become  cold  by  placing 
it  in  the  desiccator  (Fig.  19),  in  which  are  fragments  of  caustic 

alkali,  calcium  chloride,  or  sul- 
g*  phuric  acid  (caustic  soda  attracts 

water  with  the  greatest  avidity, 
next  follow  caustic  potassa  and 
calcium  chloride  in  the  order 
named).  In  the  figure,  a  is  a 
smoothly  ground  glass  plate,  with 
which  6,  a  bell-glass,  makes  an 

air-tight  joint;  c,  cup  with  concentrated  sulphuric  acid,  and  d,  the 
dish  or  crucible  with  the  precipitate  to  be  dried,  resting  upon  it. 
2.  Assays  by  volumetric  analysis1  (p.  17). — By  this  method,  the 
quantity  of  a  substance  in  solution  is  determined  from  the  volume 
of  a  solution  of  another  body,  which  produces  with  the  first  a 
definite  reaction,  and  the  strength  of  which  per  unit  of  volume 
of  its  solution  is  known  (called  a  standard  solution  or  normal 
solution).  The  result  is  then  found  by  calculation  from  the 
quantity  of  normal  solution  employed.  The  final  reaction, 
which  can  sometimes  be  recognized  only  by  a  change  occurring 
in  another  substance,  especially  added  to  the  fluid  (indicator), 
may  be  known — 

a.  In  saturating  a  base  or  an  acid  with  the  normal  solution 

1  Schwarz,  Maassanalyse,  Braunschweig,  1853  und  1873.  Schwertfeger, 
Maassanalyse,  Regensburg,  1857.  Grrager,  Maassanalyse,  Weimar,  1866. 
Fleischer,  Maassanalyse,  Leipzig,  1867.  Fleischer,  Titrirmethode,  Leipzig, 
1871.  Rieth,  Volumetric,  Bonn,  1871.  Mohr,  Titrirmethode,  Braunschweig, 
1874.  Muspratt's  Chemie,  vii.  167. 


OPERATIONS   BY   THE   WET   METHOD.  41 

(analysis  by  saturation),  by  a  change  of  color,  or  by  decolorization 
of  a  colored  solution  (assay  of  copper  with  potassium  cyanide), 
or  by  an  indicator  such  as  litmus,  which  is  added  for  the  pur- 
pose, as  in  the  estimation  of  acids  or  alkaline  carbonates. 

b.  In  precipitating  the  body  to  be  determined,  with  a  standard 
solution,  when  precipitation  ceases  (Gay  Lussac's  silver  assay),  or 
by  some  change  in  an  added  indicator  (Schaffner's  zinc  assay; 
Pelouze's  copper  assay);   and  frequently  also  by  the  drop-test, 
that  is,  a  drop  of  the  assay  fluid  and  of  the  indicating  fluid  are 
brought  in  contact  upon  a  porcelain  plate  by  means  of  a  glass-rod, 
or  alongside  of  each  other  upon  filtering  paper,  in  such  a  manner 
that  the  edges  of  the  drops  run  together,  or  by  allowing  a  drop 
of  the  assay  fluid  to  flow  down  over  paper  saturated  with  the 
indicating  substance,  etc. 

c.  In  oxidizing  or  reducing  the  substance  to  be  determined  by 
means  of  a  standard  solution  without  adding  an  indicator,  the  final 
reaction  will  be  recognized-  by  the  appearance  or  disappearance 
of  certain  colors  (chameleon  assay),  or  by  adding  an  indicator 
(starch  in  the  assay  of  copper,  assays  of  manganese,  etc.). 

The  operations  which  may  occur  are  as  follows : — 

a.  Solution,  that  is  to  say,  bringing  the  substance  to  be  tested 
into  a  state  of  solution  as  in  1,  a  (p.  35). 

b.  Preparation  of  the  standard  solution,  namely — 

a.  By  dissolving  a  weighed  quantity  of  a  chemically  pure  solid 
substance,  and  diluting  the  solution  to  a  definite  volume,  so  that 
the  chemical  power  of  a  unit  of  volume  of  the  solution  is  known. 
These  liquids  are  called  normal  solutions  when  as  many  grammes 
of  the  substance  have  been  dissolved  and  diluted  to  1  liter 
as  are  equal  to  the  atomic  weight  of  the  substance,  and  deci- 
normal  solutions  when  a  quantity  of  substance  corresponding  to 
Y1^  of  the  atomic  weight  has  been  used  for  the  solution. 

(3.  By  dissolving  an  unweighed  quantity  of  the  solid  substance 
and  making  an  empirical  solution  by  diluting  it  in  a  corresponding 
manner,  that  is  to  1  liter.  The  titer  of  this  is  determined  by 
allowing  it  to  act  upon  a  measured  volume  of  a  solution  contain- 
ing a  known  quantity  of  the  body  to  be  determined,  until  the 
reaction  takes  place.  The  titer  is  then  found  from  the  volume 
of  the  empirical  solution  consumed. 


42 


ASSAYING. 


The  standard  (titer)  of  normal  solutions  subject  to  chemical 
alterations  must  be  verified  from  time  to  time. 

G.  Measuring  and  titration  of  the  assay  liquid. — For  this  are 
required — 

a,.  For  measuring  j  stoppered  measuring  flasks  (Fig.  20)  divided 
up  to  a  mark  on  the  neck  into  1,  J-,  J-  liter  and  into  small  divis- 
ions (200, 100  cubic  centimeters,  etc.);  a  stoppered  mixing  cylinder 
(commonly  called  a  test-mixer)  (Fig.  21),  having  a  capacity  of 


Fig.  20 


from  one  to  two  liters  also  divided  into  cubic  centimeters.  By 
means  of  this,  fluids  can  be  measured  off  diluted,  and  mixed 
in  definite  proportions.  Pipettes  (measuring-pipettes)  (Fig.  22) 


OPERATIONS    BY   THE   WET   METHOD. 


43 


divided  into  whole  and  -^  cubic  centimeters ;  and  whole  pipettes, 
capable  of  holding  a  certain  number  of  cubic  centimeters  up  to 
a  mark.  The  latter  are  used  for  transferring  a  certain  quantity 
of  assay  fluid  to  a  beaker  glass,  flask,  etc.  In  doing  this  the 
lower  end  of  the  pipette  is  either  held  against  the  side  of  the 

Fig.  22. 


Fig.  23. 


25  CO 


0.5 


vessel  and  the  fluid  allowed  to  run  down  on  it,  or  it  is  held  free. 
Stohmann's  siphon-pipette  is  used  for  removing  the  clear  super- 
natant liquid  from  precipitates,  or  poisonous,  bad-smelling  liquids, 
etc. 


44 


ASSAYING. 


Fig.  25. 


-28 


50CC 


ft.  For  titrating. — Burettes1 
for  measuring  the  number  of 
cubic  centimeters  of  standard 
solution  which  have  been  al- 
lowed to  run  into  the  assay 
fluid  until  the  final  reaction  is 
reached.  For  measuring  assay 
and  normal  solutions,  it  is  a 
very  good  plan  to  place  two 
burettes  in  the  same  stand  side 
by  side.  The  burette  repre- 
sented by  Fig.  24  (p.  43)  is 
well  adapted  for  all  uses.  It  is 
provided  with  a  glass-cock  a; 
b  is  a  glass-cap  to  protect  the 
liquid  from  dust ;  c  c!  are  open- 
ings in  it  for  the  admission  of 
air.  Molir's  burette  is  the  sim- 
plest form  of  the  apparatus, 
and  has  the  preference  over  all 
others  for  general  purposes.  It- 
is,  however,  not  to  be  recom- 
mended in  cases  where  the 
rubber  of  the  pinch-cock  will 
be  liable  to  act  chemically  on 
the  liquid  employed.  (Fig.  25.) 

3.  Assays  by  colorimetric 
analysis.  —  This  method  is 
based  upon  the  principle  that 

1  Stender's  glass  manufactory  in 
Lampspringe  furnishes  graduated 
glass  vessels  with  graduation  in  red 
burned  in  with  enamel.  Konig's 
Ventilburette  in  Dingier,  ccxvii. 
134.  Kleinert's  Chameleon-burette 
in  Fresenius's  Ztschr.  1878,  p.  183. 
Biirettenstative  in  Dingier,  ccxxii. 
465  ;  ccxxix.  366.  Fresenius's 
Ztschr.  1877,  p.  82,  228. 


MUFFLE-FURNACES.  45 

equal  volumes  of  solutions  of  an  equally  intense  color  contain 
also  equal  quantities  of  coloring  matter.  By  comparing  fluids  ot 
an  equal  intensity  of  color,  and  taking  the  volume  into  considera- 
tion, a  conclusion  is  formed  as  to  the  percentage  of  the  coloring 
body  which  is  contained  in  the  one  to  be  determined.  The  same 
manipulations  occur  here  as  in  assays  by  gravimetric  analysis, 
namely,  solutions,  precipitation,  etc.,  and  in  addition  comparison 
of  the  colored  assay  solution  with  standard  colored  solutions  con- 
tained in  tubes  or  tapering  glasses  of  known  cross-sections,  meas- 
uring the  solutions  in  calibrated  cylinders,  etc. 

Ill,  Assay  Furnaces, 

9.    GENERAL   REMARKS. 

The  choice  of  an  assay  furnace  will  depend  chiefly  on  the 
degree  of  heat  to  be  obtained,  and  whether  the  substances  are  to 
be  oxidized  or  reduced,  or  only  calcined,  fused,  sublimed,  or  dis- 
tilled. Furnaces,  accordingly,  are  divided  into  muffle  furnaces, 
draught  or  wind  furnaces,  blast  furnaces,  sublimation  furnaces, 
and  distillation  furnaces.  In  regard  to  their  construction,  they 
vary  chiefly  according  to  the  fuel  to  be  used  (flaming  or  glowing 
fuel). 

10.    MUFFLE-FURNACES.1 

The  principal  part  of  this  is  the  muffle  (Fig.  26).  It  is  usually 
made  of  refractory  clay,  sometimes,  though  rarely,  of  iron.  It 
is  open  in  front,  and  closed  at  the  rear ;  and  the 

semi-cylindrical  body  is  often  provided  along  the  ^^ 

sides  with  draft  orifices,  as  shown.  It  is  either  (fj\  Q  Q  | 
connected  with  the  bottom,  or  stands  loose  upon  it. 
It  serves  for  the  reception  of  the  assay  charge,  and  is  heated  from 
the  outside  by  a  glowing  or  flaming  fire.  These  furnaces  are 
absolutely  necessary  for  oxidizing  processes  (calcining,  cupella- 
tion,  refining),  but  they  are  also  adapted  for  operations  requiring 

1  Engin.  and  Min.  Journ.  1878,  No.  26,  p.  443.  Sillimau,  Double  Muffle- 
Furnace,  1876,  vol.  xxii.  No.  17. 


46  ASSAYING. 

only  the  production  of  a  high  temperature  (glowing,  reducing, 
and  purifying  fusion,  etc.),  that  is  to  say,  when  only  temperatures 
not  exceeding  the  fusing  point  of  gold  and  copper  (about  1200°  C., 
2192°  F.)  are  required  (they  are,  therefore,  not  available  for 
assays  of  cast-iron).  In  the  latter  cases  the  fuel  is  not  completely 
utilized,  and  besides,  they  are  more  difficult  to  attend  than  the 
wind  and  blast  furnaces,  where  the  crucibles,  etc.,  are  placed 
directly  in  the  glowing  fire,  or  come  in  direct  contact  with  the 
flame. 

The  furnaces  are  either  bricked  in  (for  instance,  large  muffle- 
furnaces  for  burning  coal),  or  they  are  portable.  In  the  latter 
case,  the  furnace  for  receiving  the  muffle  is  constructed  of  fire- 
clay which  is  sometimes  surrounded  with  a  casing  of  sheet-iron 
(mint  furnaces).  The  work  connected  with  the  muffle-furnace 
consists  chiefly  in  heating  it,  regulating  the  temperature  (by  re- 
ducing or  urging  the  fire,  regulating  the  admission  of  air,  opening 
or  closing  the  mouth  of  the  muffle,  by  removing  or  piling  up 
fuel,  etc.),  in  stirring  the  fire  regularly  (in  doing  this  the  fuel 
must  be  piled  chiefly  upon  the  front  part  of  the  grate  and  only  a 
thin  layer  upon  the  back  part),  in  ventilating  the  grate  frequently, 
in  repairing  (that  is,  lining  defective  places  in  the  walls  of  the 
furnace,  filling  in  of  cracks  in  the  bottom  of  the  muffle  with  fire- 
clay, or  scraping  the  bottom  and  lining  it  by  strewing  it  with 
powdered  fire-clay,  cupel  ashes,  chalk,  pounded  assay  vessels, 
etc.),  introducing  and  removing  the  assay  vessels  in  the  muffle, 
cleansing  the  furnace  after  the  work  is  finished  by  drawing  the 
glowing  cinders  from  the  grate  and  allowing  the  fire-door  to 
remain  open,  etc. 

According  to  the  kind  of  fuel  used,  we  may  divide  them  into — 
1.  Furnaces  for  solid,  free-burning,  flaming  fuel. — These  are 
generally  used  with  large  muffles,  and  with  such  fuel  the  heat 
can  be  better  regulated  than  in  furnaces  heated  by  a  glowing 
fire,  but  they  require  more  care  in  attending  them.  Stoking  is 
done  from  the  front  (Plattner's  furnace1),  or  from  the  back 
(Schemnitz,  Pribram2).  With  the  latter  arrangement  the  opera- 

1  Freiberger,  Jahrb.  1842,  p.  1.      Ztschr.  des  Ver.  deutsch.  Ingen.  1877, 
Plate  12,  Figs.  3  to  5. 

2  Rittinger's  Erfahr.  1857,  p.  29.     B.  u.  h.  Ztg.  1876,  p.  353  ;  1876,  p.  61. 


MUFFLE-FURNACES. 


47 


tor,  working  in  front  of  the  furnace,  is  not  exposed  to  the  direct 
heat,  but  it  also  prevents  him  from  giving  immediate  attention  to 
the  firing  should  the  assay  require  it. 

Fig.  27. 


Fig.  27  represents  Plattner's  muffle-furnace  for  coal,  with  the 
stoke-hole  in  front,     a,  muffle  of  fire-clay,  36.6  centimeters  long, 


48 


ASSAYING. 


17.6  centimeters  high,  and  34.2  centimeters  wide,  with  an  ascend- 
ing slope  of  2.4  centimeters.  It  rests  upon  the  support  6,  and 
three  legs  e;  d  is  the  vault.  There  is  a  space  of  4.9  centimeters 
between  it  and  the  walls  of  the  furnace,  e,  the  chimney,  14.7 
centimeters  wide,  and  3  to  4  meters  high.  /,  mouth  of  the  muffle, 
12  centimeters  wide,  and  14.6  centimeters  high,  which  can  be 
closed  by  the  fire-clay  door  g.  Another  door  h  is  used  for  cover- 
ing a  slit  sometimes  provided  over  the  muffle  (for  heating  plates 
of  metal,  etc.),  but  it  is  usually  omitted ;  i  is  the  grate,  26.8 
centimeters  wide,  and  .51.4  centimeters  long,  28.1  centimeters 
below  the  muffle;  k,  the  stoke-hole,  22  centimeters  high,  and 
26.8  centimeters  wide;  /,  fire-door;  w,  ash-pit,  76.8  centimeters 
long,  and  26.8  centimeters  wide;  n,  a  channel,  22  centimeters 


Fig.  28.    , 


Fig.  29. 


wide,  communicating  with  the  open  air  for  conducting  air  under 
the  grate  through  the  flue  o,  p,  9.8  centimeters  wide,  which  is 
provided  with  a  damper  q  ;  r,  ash-pit  door,  26.8  centimeters 
wide,  and  34.2  centimeters  high. 


MUFFLE-FURNACES. 


49 


Figs.  28  and  29  represent  a  muffle-furnace  with  the  stoke-hole  at 
the  back,  a,  muffle,  resting  upon  the  supports  c  and  c';  6,  mouth 
of  the  muffle ;  d,  front  wall ;  e,  grate ;  /,  fire-door ;  /',  fire-box  ; 
g,  refractory  lining ;  h,  i,  channel  for  conducting  the  external  air 
beneath  the  grate ;  k,  damper ;  I,  ash-pit  door ;  I',  ash-pit ;  m,  fire- 
space  surrounding  the 'muffle;  m',  chimney  (it  is  better  to  place 
it  nearer  d),  with  damper  n,  nf,  and  lever  o,  for  regulating  the 
same ;  p,  brickwork  of  the  chimney,  with  flues,  r,  for  carrying 
off  the  fumes  coming  from  the  mouth  of  the  muffle;  q,  hooping. 

2.  Charcoal  and  coke  furnaces. — Coke,  as  a  general  rule,  re- 
quires a  grate  under  the  muffle,  and  a  strong  draught.  With 
charcoal  this  arrangement  is  not  so  essential,  though  in  order  to 
secure  a  more  uniform  supply  of  air  a  grate  is  usually  provided. 
The  ashes  from  coke  are  more  difficult  to  remove  and  attack  the 
walls  of  the  furnace  more  than  wood  ashes.  Smaller  furnaces 
of  this  kind  are  much  used  for  assaying  gold  and  silver ;  and 
also  larger  ones,  in  which  the  heat  can  be  better  regulated  (the 
Schemnitz  charcoal  furnaces  are  of  this  construction),  and  where 
the  stoke-hole  is  in  the  rear,  or  the  firing  is  done  through  two 
channels  on  the  sides. 

Assay  furnaces  for  charcoal. — Fig.  30  shows  such  a  furnace. 
6,  muffle  of  fire-clay,  14  centimeters  long,  7.5  centimeters  high, 
9  centimeters  wide,  with  walls 
8  millimeters  thick,  and  rest- 
ing  upon    two   rails    passing 
through  openings  in  the  iron 
casing.    The  inside  of  the  cas- 
ing is  lined  with  fire-clay  from 
1 5  to  20  millimeters  thick.    In 
front  of  the  muffle  is  a  shelf 
of  sheet-iron  resting  upon  the 
rails    supporting    the   muffle; 
c  is  the  mouth  of  the  furnace 
through  which  the  charcoal  is 
fed,  and  the  products  of  com- 
bustion escape  into  a  hood  or  through  a  sheet-iron  smoke-stack. 
The  mouth  of  the  muffle  and  the  flues  above  and  below  it  can 
be  closed  by  dampers ;  a,  the  cupel. 
4 


50 


ASSAYING. 


3.  Gas  furnaces  (coal-gas). — By  using  these  furnaces  the  work 
can  be  carried  on  in  a  very  cleanly  manner,  and  the  temperature 
can  be  very  perfectly  regulated.  The  gas  is  introduced  either  by 
means  of  burners  placed  at  the  rear  wall  (Perrot's  furnace,  used 
in  the  Berlin  School  of  Mines),  or  from  below  through  four 
straight  burners  standing  alongside  each  other  beneath  a  slit  in 
the  bottom  (furnaces  of  Lenoir  and  Forster  of  Vienna,  used  in  the 
laboratory  of  the  Schemnitz  School  of  Mines,  etc.),  or  through 
curved  burners  arranged  in  the  form  of  a  circle  beneath  the 
furnace  (furnace  of  the  Societe  genevoise  pour  la  construction 
d'instruments  de  physique  i  Geneve,  used  in  the  Berlin  School 
of  Mines).  The  oil  furnaces  of  Andouin-Devitte  of  Paris  (using 
the  vapors  of  crude  petroleum)  are  said  to  be  cheaper  in  opera- 
tion than  the  gas  furnaces  just  described.  The  oil  trickles  from 
funnels  upon  the  hot  grate-bars  set  obliquely  and  channelled. 
There  it  is  instantly  vaporized  and  burns.1 

Fig.  31  shows  Perrofs  gas  muffle-furnace,  a,  muffle  of  fire- 
clay, with  refractory  coating  and  movable  cover  6  ;  e,  /,  </,  furnace 

Fig.  31. 


walls  of  sheet-iron  with  refractory  lining ;  A,  burner,  with  cham- 
ber p,  into  which  coal-gas  enters  at  o,  from  the  pipe  u9  provided 
with  manometer  v.  From  here  it  passes  through  narrow  chan- 

1  Ztschr.  des  Ver.  deutsch.  Ingen.  xxi.  225. 


DRAUGHT   OR   WIND   FURNACES. 


51 


nels  into  the  burner-tubes  q  and  r,  which  are  provided  below 
with  openings  furnished  with  valves  t  for  regulating  the  admis- 
sion of  air ;  w,  w,  the  nozzles  from  which  the  flame  passes  through 
d  into  the  space  around  the  muffle,  and  escapes  through  the  flue 
k  into  the  chimney  I,  in  which  is  a  damper  m.  The  chimney  also 
receives,  through  the  pipe  n,  the  fumes  which  may  escape  from 
the  mouth  of  the  muffle. 


Fig.  32. 


11.    DRAUGHT  OR  WIND  FURNACES. 

These  consist — 

1.  In  case  carbonized  fuel  (coke,  charcoal)  is  used,  of  a  round, 
rectangular  or  oblong  fire-place,  separated  from  the  ash-pit  at  the 
base  by  a  grate,  and  provided  with  a  fire-clay  or  cast-iron  cover 
or  top-plate.  A  lateral  flue  connects  the  fire-place  with  the 
chimney.  The  furnace  is  either  bricked  in  (Fig.  32)  or  is  porta- 
ble. In  the  latter  case,  the  body  of  the  furnace  is  made  of  a 
sheet-iron  cylinder  lined  with  re- 
fractory material.  It  is  also  a  very 
good  plan  to  set  a  furnace  of  this 
kind  into  brick-work,  leaving  an 
intermediate  space  between  the  two, 
in  which  case  the  usual  binding 
with  strap-iron  may  be  dispensed 
with.  The  cover  or  top-plate  over 
the  fire-place  consists  of  two  fire- 
tiles  provided  with  some  conveni- 
ence for  easily  removing  and  re- 
placing them.  It  is  best  to  place 
a  small  carriage  in  the  ash-pit 
(Fig.  33)  for  receiving  and  remov- 
ing the  ashes  (Berlin  School  of 

Mines).  The  degree  of  temperature  possible  to  attain  depends 
on  the  height  of  the  shaft  between  the  grate  and  the  flue,  the 
height  of  the  chimney,  and  the  quality  of  the  fuel  used  (coke  will 
give  a  higher  temperature  than  charcoal).  The  temperature  can 
be  increased  with  the  aid  of  a  flue  leading  from  the  ash-pit  into 
the  open  air,  or  by  an  under-grate  blast,  and  is  regulated  by  a 


52  ASSAYING. 

damper  fixed  in  the  door  of  the  ash-pit,  or  in  the  flue  or  chimney. 
The  highest  temperature  is  found  at  about  4  to  6  centimeters 
above  the  grate,  which  should  be  taken  into  consideration  in 
placing  the  crucibles  in  the  furnace. 

The  labor  attending  these  furnaces  consists  of — 

a.  The  placing  of  the  assay  vessels  in  the  furnace  by  hand. 
If  it  is  necessary  to  look  into  them  during  the  operation  (assay 
of  lead  in  iron  crucibles,  Cornish  roasting  assay  of  copper),  they 
are  placed  in  a  hollow  made  in  the  fuel,  generally  coke ;  or,  if 
this  is  not  required  (assays  for  lead,  copper,  tin,  iron,  etc.,  in  clay 
crucibles),  the  assay  vessels   are  placed  immediately  upon  the 
grate,  leaving  sufficient  space  between  them  for  the  necessary 
fuel,  and  in  such  a  manner  that  the  part  of  the  vessel  which  is 
to  be  heated  the  strongest  stands  about  4  to  6  centimeters  above 
the  grate.     If,  therefore,  vessels  with  feet  are  used,  they  must  be 
placed  directly  upon  the  grate,  while  those  without  feet  (crucibles) 
are  supported  on  a  block  or  stand  of  fire-clay. 

b.  Firing. — This,  as  a  general   rule,  is  done  from  below   by 
putting  glowing  coals  between  the  assaying  vessels,  filling  up  the 
shaft  with  fuel,  and  then  gradually  closing  the  top-plate  of  the 
furnace.     But  if  the  heating  must  take  place  very  slowly,  the 
firing  is  done  from  above,  by  placing  the  glowing  coals  on  top  of 
the  fuel  with  which   the  shaft   is  filled.     The  fire,  when   the 
mouth  of  the  furnace  is  closed,  will  then  gradually  work  down. 
(In  the  Schemnitz  laboratory,  the  lateral  flue  is  placed  below  the 
grate  and   the  air  required  for  combustion    is  introduced  from 
above.)     The  temperature  is  regulated  in  the  manner  indicated 
on  p.  51,  and,  if  necessary,  fuel  is  added  from  time  to  time,  but, 
before  this  is  done,  the  glowing  coal  must  be  poked  down  to  do 
away  with  empty  spaces. 

c.  Taking  the  vessels  from  the  furnace. — This  is  done  by  lifting 
the  vessels  out  at  the  top  of  the  furnace,  by  means  of  crucible 
tongs  (Fig.  60),  either  out  of  the  coke,  or  from  the  grate,  after 
the  fuel  has  burned  down,  or,  in  the  latter  case,  it  may  be  more 
convenient  to  remove  them  through  an  opening  in  the  side  (t  in 
Fig.  32),  but  this  must   be  closed  up  during  the  operation  of 
the  furnace.     Either  the  contents  of  the  crucibles  are  poured  out 
and  the  crucibles  while  still  glowing  placed  back  in  the  furnace 


DRAUGHT   OR   WIND   FURNACES. 


53 


and  again  charged  from  the  mixing  capsules  (Fig.  7)  (assay  of 
lead  in  an  iron  crucible),  or  the  clay  crucibles  are  allowed  to  cool 
off  and  are  then  broken  up. 

Fig.  33. 


Fig.  34. 

The  furnaces  used  in  the  Berlin  School  of  Mines  are  shown  in 
Figs.  33,  34,  and  35.  They  consist  of  an  iron  cylinder  A  set 
into  brick- work  and  lined  with  refractory  material.  The  grate 


54 


ASSAYING. 


Fig.  36. 


DRAUGHT   OR   WIND   FURNACES.  56 

forms  the  bottom,  beneath  which  is  placed  a  truck  B  for  the 
ashes.  The  door  of  the  ash-pit  C  is  provided  with  register  F. 
D  represents  the  flue  and  E  the  chimney.  The  height  of  the 
furnaces  varies  according  to  the  kind  of  assays  to  be  made  in 
them.  The  refractory  lining  is  usually  about  5  centimeters  in 
thickness,  giving  the  furnace  a  clear  interior  diameter  of  about 
34  centimeters.  For  lead  assays  they  are  20  centimeters  high, 
for  copper  26  centimeters,  and  for  iron  35.5  centimeters.  The 
chimney  is  10  meters  high,  provided  with  a  damper  for  regu- 
lating the  draught.1 

2.  Wind  furnaces  for  free-burning  (flaming)  coal. — The  assay 
vessels  stand  over  the  grate  upon  a  tile  of  fire-clay  in  the  same 
manner  as  in  Plattner's  furnace,  except  that  there  is  no  muffle. 
(Freiberg.) 

3.  Wind  furnaces  for  illuminating  gas.2 — These  furnaces  are 
easily  attended,  the  work  can  be  carried  on  in  a  very  cleanly 
manner,  and  at   the  same   time  with   the  greatest  accuracy,  as 
the  assayer  can  conveniently  look  into  the  crucible  during  the 
operation. 

Fig.  36  represents  Perrot's  furnace,  a,  the  outer  shell,  with 
cover  bj  and  sight-hole  c;  d,  the  crucible,  upon  a  movable  stand, 
e  •  /,  inner  shell ;  g,  pipe,  with  manometer  h,  and  cock  i,  for 
conveying  gas  into  the  annular  chamber  k,  from  which  it  passes 
through  the  pipes  I,  through  the  annular  opening  m,  into  the 
inner  space  of  the  furnace,  where  flame  plays  around  the  crucible 
d,  and  finally  escapes  through  the  upper  opening  of  the  inner 
chamber  into  the  exterior  annular  space,  and  is  carried  off  below 
through  the  pipe  n,  leading  to  the  chimney ;  o,  openings  for 
admitting  the  air  required  for  combustion,  which  is  mixed  in  the 
pipes  I  with  the  gas.  The  admission  of  air  is  regulated  by  a 
cut-off,  p  is  a  cup  for  the  reception  of  any  metal  which  may 
overflow  and  escape  from  the  crucible. 

i  B.  u.  h.  Ztg.,  1880,  p.  2. 

*B.  u.  h.  Ztg.  1873,  p.  284  (Perrot)  ;  Dingier,  ccvi.  360  (Wiessnegg); 
Dingier,  clxxx.  220;  clxxxix.  376;  Oestr.  Jahrb.  v.  Hauer,  1878,  p.  123 
(Schlosing).  Mitchell,  Pract.  Assaying,  1888,  pp.  74  to  105.  Heinpel's 
Gasofen  mit  Oxydationsvorrichtung,  z.  B.  zum  Abtreiben,  in  Fresenius's 
Ztsclir.  xvi.  454  ;  xviii.  404  (may  be  had  of  Desaga  in  Heidelberg). 


ASSAYING. 


Wiessnegg's  gas  furnaces  are  of  simpler  construction,  and  con- 
sume less  gas.     The  flame  plays  around  the  crucible  in  the  form 

Fig.  37. 


of  a  spiral.  By  this  means  air  and  gas  are  more  intimately 
mixed,  and  higher  temperatures  can  be  obtained.  The  same 
result  is  attained  in  Schlosing's  furnace.  The  attainable  heat  of 
Parrots  furnace  is  about  1560°  C.  (2840°  F.). 

.  Roessler1  describes  a  small  furnace  for  the  production  of  high 
temperatures  (Fig.  37)  which  is  heated  by  a  Bunsen  burner  A 
considerable  quantity  of  pure  gold,  silver,  etc.,  can  be  melted  in  it 
in  from  fifteen  to  twenty  minutes.  The  cold  air  enters  at  e  and  is 
heated  by  the  hot  walls  of  the  sheet-iron  jacket  d.  It  then  passes 

1  Polytechn.  Notizblatt,  1884,  p.  308.     Chemikerztg,  1884,  p.  1220. 


DE AUGHT  OB  WIND  FURNACES. 


57 


to  the  burner  and  thence  towards  the  top  at  a  into  the  flame  and 
together  with  the  latter  under  the  crucible  6  where  combustion 
takes  place.  The  products  of  combustion  pass  out  through  the 
aperture  v,  through  the  iron  jacket,  and  after  heating  its  inner 
walls,  are  carried  off  through  the  chimney  g.  Beneath  the  latter  is 
placed  a  second  burner  whose  flame  has  to  be  so  regulated  that 
only  sufficient  air  for  complete  combustion  is  drawn  in. 

For  melting  with  a  coke-fire  the  same  principle  has  been  mod- 
ified as  shown  in  Fig.  38.  The  cold  air  enters  at  a  and  after 
being  heated  passes  through  c  into  the  closed  ash-pit  under  the 


Fig.  38. 


grate.  The  products  of  combustion  escape  through  d,  deposit  at  e 
any  dust  or  ashes  they  may  contain,  and  after  heating  the  air  for 
combustion  passes  out  through  the  chimney.  By  this  preparatory 
heating  the  air  acquires  a  temperature  of  nearly  300°  C.  (572°  F.) 
and  a  combustion  temperature  of  about  1400°  C.  (2552°  F.).1  The 
tightly  closed  ash-pit  door  is  shown  at/*. 

Fig.  39  shows  Fletcher's  direct  draft  crucible  furnace.  It  con- 
sists of  a  fire  clay  body  held  together  by  sheet-iron  bands.  The 
heat  and  flame  pass  through  the  body  of  the  furnace  to  the  chim- 
ney. It  can  be  used  either  for  scorifying  or  cupelling,  and  by 
removing  the  top  cover  the  heat  has  full  play  upon  a  roasting  dish 
placed  upon  it. 

1  Dingler's  Journ.  Bd.  257,  p.  153.     Chemikerztg,  1885,  p.  1359. 


58 


ASSAYING. 


Fig.  40  is  a  new  form  of  gas  furnace  suggested  by  Brown.1     In 
this  furnace  the  flame  from  the  burner,  shown  in  the  left  of  the 

Fig.  39. 


Fig.  40. 


engraving,  rises  and  passes  horizontally  through  the  body  of  the 
furnace  to  the  chimney.   Its  form  and  operation  are  somewhat  similar 

1  Manual  of  Assaying.     Walter  Lee  Brown.     Chicago,  1886. 


BLAST    FURNACES.  59 

to  those  of  a  reverberatory  furnace,  the  movable  bricks  when  in 
place  forming  the  roof.  The  exterior  dimensions  are  20  inches 
(50.6  centimeters)  long,  7  inches  (17. 71  centimeters)  wide,  and  5^ 
inches  (13.91  centimeters)  deep.  In  the  interior,  upon  the  bottom, 
are  four  little  wedge-shaped  bridges  of  fire-clay  which  are  movable  ; 
and  upon  these  rests  a  false  bottom,  also  movable.  The  latter 
corresponds  to  the  muffle-bottom  of  an  ordinary  furnace,  and  upon 
it  is  done  all  the  work. 


12.    BLAST  FURNACES. 

These  are  low  cylindrical  shaft  furnaces,  constructed  of  fire- 
resisting  material,  or  of  a  sheet-iron  cylinder  lined  with  refrac- 
tory clay.  At  some  distance  above  the  hearth  of  the  furnace 
are  one  or  several  tuyeres  symmetrically  arranged.  The  mouth 
of  the  furnace  is  provided  with  a  movable  sheet-iron  chimney. 
The  furnace,  in  order  to  increase  the  temperature,  is  well  sup- 
plied with  air  heated  in  the  space  between  the  two  iron  shells 
surrounding  the  shaft  (Sefstrom's  furnace)  or  in  a  reservoir  below 
the  perforated  hearth  of  the  furnace  (Devillefs  furnace).1  The 
hearth  in  Welch's  furnace  may  be  easily  separated  from  the 
furnace  body.2  The  fuel  used  in  these  furnaces  should  be  in 
lumps  about  the  size  of  a  walnut  and  uniform  in  size.  A  very 
high  temperature  can  be  produced  in  a  shorter  time,  and  with 
the  consumption  of  less  glowing  fuel  than  in  wind  furnaces,  but 
a  certain  amount  of  power  is  required  for  operating  the  blast 
(bellows,  fan,  Root's  blower),3  and  the  fire  must  frequently  be 
stirred  and  fuel  added.  If  only  one  crucible  is  used,  it  is  placed 
in  the  centre  of  the  furnace.  But  if  more  are  placed  in  the  fur- 
nace at  one  time,  each  is  placed  at  the  same  distance  from  one  of 
the  tuyeres.  Raschette's  furnace  furnishes  very  high  temperatures  ; 
it  has  an  oblong  cross-section,  and  the  tuyeres  are  arranged 
alternately  in  rows.  Munscheid's4  gas  blast  furnaee  gives  also 
very  high  temperatures.  Gas  and  air  mixed  are  drawn  into  it 
by  means  of  an  exhaust  fan. 

1  Kerl,  Thonwaarenindustrie,  1879,  p.  76.  2  Dingier,  ccxxix.  159. 

8  Root's  blowers  are  well  adapted  for  this  purpose. 
4  B.  u.  h.  Ztg.  1878,  p.  361. 


60 


ASSAYING. 


Fig.  41. 


Fig.  41  shows  Sef strom's  furnace,     b  is  the  space  between  two 
sheet-iron  cylinders  closed  on  top  by  a.     The  inner  cylinder  is 

lined  with  a  fire-resisting  mate- 
rial, c  (1  part  clay  and  3  to  4 
parts  quartz  sand).  The  air 
enters  at  d,  and,  after  having 
been  heated  in  the  intermediate 
space,  is  carried  through  the 
tuyeres  o.  The  dimensions  of  a 
furnace  for  six  small  iron  cruci- 
bles are  as  follows  :  18  centime- 
ters in  diameter;  total  height  15 
centimeters ;  a  collar  7  centime- 
ters high,  upon  which  sits  the 
sheet-iron  chimney;  width  and 
height  in  the  clear,  10.5  centi- 
meters ;  thickness  of  the  refractory  lining  2.5  centimeters ;  dis- 
tance between  the  two  cylinders,  on  the  sides  1.2  centimeters, 
and  on  the  bottom  2.5  centimeters.  The  manometer  is  placed 
on  the  exterior  shell.  Lang's  blast-furnace1  for  larger  masses 
has  an  annular  air-conduit. 

Fig.  42. 


Fig.  42  shows  Fletcher's  injector  gas  furnace.  It  consists  of  a 
hollow  cylinder  of  fire-clay  inclosed  in  a  sheet-iron  casing  arid  con- 
taining an  interior  space  sufficiently  large  to  hold  a  crucible  about  3 


Karntlm.  Ztschr.  1879,  No.  8,  p.  287. 


FURNACES   FOR   SUBLIMATION   AND   DISTILLATION. 


61 


inches  (7.58  centimeters)  in  diameter.  Extremely  high  tempera- 
tures can  be  obtained  in  this  little  furnace,  when  a  free  supply  of 
gas  is  introduced  through  the  blast  burner. 


13.    FURNACES  FOR  SUBLIMATION  AND  DISTILLATION. 

These  consist  of  a  fire-space  to  be  heated,  for  the  reception  of 
variously  shaped  vessels  (tubes,  retorts,  boilers,  etc.)  of  clay, 
porcelain,  glass,  or  iron,  in  which  the  substances  are  heated 
without  addition  (as,  arsenical  pyrites,  iron  pyrites,  amalgam), 
or  with  fluxes  (preparation  of  realgar,  separation  of  mercury 
from  cinnabar,  etc.).  They  are  usually  provided  with  a  receiver, 
cooled  oif,  for  condensing  the  volatile  products  into  solid  bodies 
(sublimation),  or  to  fluids  (distillation). 

Fig.  43  shows  a  sublimation  furnace,  a  are  clay  tubes  for  the 
reception  of  the  assay  sample  (as,  for  example,  arsenical  pyrites 
or  iron  and  arsenical  pyrites  for  the  production  of  realgar); 
6,  receiver  for  the  sublimate  (arsenic,  realgar) ;  c,  the  grate ;  d,  flues. 


Fig.  43. 


Fig.  44. 


Fig.  44  represents  a  distillation  furnace,  a,  tube  for  the  recep- 
tion of  the  assay  sample  (for  instance,  gold  or  silver  amalgam) ; 
e,  grate;  h,  combustion  chamber;  g,  chimney;  c,  pipe  for  carry- 
ing off  vapors  (of  mercury)  into  the  condensing  pipe 'k,  provided 
with  a  funnel  /,  the  edge  of  which  is  covered  with  a  cloth  </,  upon 
which  cold  water  flows  from  n,  and  overflows  at  o. — Or  Fig.  45. 


62 


ASSAYING. 


a,  a  retort,  with  tubulure  b;   c,  receiver,  covered  with  paper  or 
cloth  kept  cool  by  water  which  is  allowed  to  trickle  upon  it. — 

Fig.  45. 


Fig.  46. 


Or  Fig.  46,  if  a  more  thorough  cooling  off  is  required,     h,  a  re- 
tort, from  which  the  vapors  pass  through  i  into  the  cooling-pipe  a. 


OF  THF 

UNIVERSITY 

ASSAY   VESSELS   FOR   THE   DRY   METHOD.  (J{ 

This  rests  upon  a  stand  g,  and  is  surrounded  by  a  sheet-iron 
cylinder,  into  which  cold  water  passes  through  e,  and  is  dis- 
charged at  c,  /,  while  the  liquid  formed  from  the  condensed 
vapors  is  collected  in  b. 

Organic-combustion  furnaces  (Fig.  77)  may  also  be  used  for 
heating  tubes. 

IV,  Assay  Vessels, 

14.    GENERAL  REMARKS. 

The  form  of  the  assay  vessels,  as  well  as  the  materials  from 
which  they  are  made,  varies  according  to  the  object  for  which 
they  are  to  be  used.  The  principal  distinction  is,  whether  they 
are  to  be  employed  in  the  dry  or  wet  method. 

15.    ASSAY  VESSELS  FOR  THE  DRY  METHOD. 

A.  Clay  vessels.1 — These  are  required  to  be  more  or  less  refrac- 
tory according  to  the  heat  to  which  they  are  to  be  exposed  (their 
refractory  quality  depends  on  the  proportion  between  silicic  acid 
and  alumina  and  the  quantity  of  fluxing  agents — ferric  oxide, 
lime,  alkalies,  magnesia — which  may  be  present).  They  must 
allow  of  being  suddenly  heated  and  cooled  without  cracking  (fat, 
contracting  clay  requires  to  be  mixed  with  quartz,  chamotte,2 
graphite).  The  vessels  should  be  corroded  as  little  as  possible 
by  the  substances  heated  in  them,  but,  as  a  general  rule,  this  can 
never  be  entirely  prevented.  (It  may  be  done  to  some  extent  by 
making  the  sides  of  the  crucible  thicker,  or  by  giving  a  finer 
grain  to  the  stuff  of  which  they  are  made.  This  should  be  made 
as  compact  as  possible,  by  mixing  the  clay  with  chamotte  instead 
of  quartz.  The  interior  of  the  crucible  should  be  made  very 
smooth,  and  it  should  be  fired  in  the  kiln  as  strongly  as  possi- 
ble.) The  vessels  should  further  be  very  compact.  This  can  be 

1  Kerl,  Thonwaarenindustrie,   1879,  p.  491.      Percy,   Metallurgy,  vol.   I. 
1875,  p.  111. 

2  [Chamotte  is  a  mixture  of  unburnt  fire-clay  and  dust  of  fire-bricks,  glass 
pots,  or  seggars. — TRANSLATOR.] 


64 


ASSAYING. 


accomplished  by  giving  a  suitable  grain  to  the  mass,  exercising 
great  care  in  moulding  and  firing  them  strongly.  The  compact- 
ness of  the  vessels  is  tested  by  fusing  metallic  sulphides,  such  as 
galena,  several  times  in  them.  They  are  made  either  by  a  plw/ 
and  mould  (roasting  dishes  and  scorifiers,  Upper  Harz  crucibles 
for  lead  smelting)  or  they  are  turned  upon  the  potter's  wheel 
(crucibles  and  larger  melting  pots). 

The  principal  vessels,  etc.,  are — 

1.  Vessels  without  feet. 

a.  Roasting  dishes  (Fig.  8). — They  are  flat,  smooth  inside,  not 
very  refractory,  8  to  10  millimeters  deep  and  50  to  80  millime- 
ters wide.     They  are  used  in  the  manner  indicated  on  p.  32. 

b.  Scarification  or  calcining  vessels  (Fig.  47). — They  have  a 
thick  bottom  and  sides,  very  smooth  interior,  and  are  very  com- 
pact.    To  avoid  being  corroded  by  lead  oxide, 
they  should  be  made  of  clay  mixed  with  cha- 
motte.     They  are  40  to  50  millimeters  wide  in 
the  clear,  15  to  20  millimeters  deep,  with  a  bot- 
tom 10  millimeters  or  more  thick. 

c.  Refining  dishes. — They  have  either  the  same  form  as  the  flat 
roasting  dishes,  but  are  fire  resistant  and  one  edge  is  somewhat 
ground  down,  or  they  are  made  from  fragments  (Fig.  48)  of 
crucibles  (Fig.  52),  and  are  then  70  to  80  millimeters  long ;  or 
they  are  shaped  like  a  flat  saucer  with  feet.     These  are  30  milli- 
meters wide,  with  a  total  height  of  25  millimeters  (Hungary). 

d.  Crucibles. — These  are  of  various  forms  and  sizes,  large  and 
small  (Figs.  49  to  51).     They  are  respectively  32  and  45  milli- 


Fig.  47. 


Fig.  48. 


Fig.  49. 


Fig.  50. 


Fig.  51. 


meters  high  in  the  clear,  and  have  a  total  height  of  39  and  52 
millimeters,  a  clear  width  of  33  and  43  millimeters,  and  are  not 
very  refractory.  Fig.  50  shows  a  large  and  a  small  Cornish 


ASSAY   VESSELS   FOR   THE   DRY   METHOD. 


65 


crucible  for  the  assay  of  copper.  They  are  very  refractory. 
Their  respective  dimensions  are :  diameter  on  the  top  80  and 
68  millimeters,  total  height  84  and  60  millimeters.  Fig.  51 
represents  a  crucible  for  iron.  This  is  lined  by  means  of  a 
wooden  plug  with  charcoal  powder,  b  (this  is  first  moistened  with 
starch  paste,  molasses,  or  clay),  or  it  is  lined  with  a  mixture  of 
90  to  95  per  cent,  retort  graphite,  5  per  cent,  rosin,  and  some 
petroleum,  and  burned  with  exclusion  of  air.  They  are  covered 
with  the  perforated  lid  c.  They  are  37  millimeters  high  and  25 
millimeters  wide,  and,  after  they  have  been  lined,  respectively 
22  millimeters,  and  10  millimeters.  They  are  very  refractory 
(Hessian  pots).  The  French  pots  are  especially  refractory  and 
smooth  inside. 

Graphite  crucibles  are  made  of  graphite  mixed  with  clay.  They 
are  very  smooth  inside,  and  very  refractory.  Those  used  in 
Cornwall  for  assay  of  tin  are  80  millimeters  wide  on  the  top,  and 
50  millimeters  on  the  bottom,  have  a  clear  height  of  74  milli- 
meters, and  a  total  height  of  90  millimeters. 

Soapstone  crucibles,  if  gradually  heated,  are  adapted  for  all 
smelting  purposes.  They  are  infusible,  not  affected  by  alkalies, 
and  become  harder  by  burning. 

2.  Vessels  with  feet.     Crucibles  for  lead  and  copper  smelting  (a, 
Fig.  52). — The  latter  are  more  refractory  than  the 

first.  They  are  25  to  32  millimeters  wide  on  the 
top,  40  to  50  millimeters  in  the  centre,  83  to  85 
millimeters  high  in  the  clear,  with  a  total  height  of 
110  to  120  millimeters.  Sometimes  there  is  a  de- 
pression in  the  bottom  for  the  reception  of  the  regu- 
lus,  and  the  foot,  when  broken  off,  may  serve  as  a 
cover. 

Fig.  53  shows  a  crucible  for  smelting  iron,  lined 
with  powdered  charcoal  (see  above).  These  crucibles 
are  45  millimeters  wide,  and  55  millimeters  high  in 
the  clear,  with  a  total  height  of  90  millimeters. 

3.  Other   clay   vessels. — To   this   category  belong 
muffles  (p.  45),  retorts,  and  tubes. 

B.    Wrought-iron   vessels.     Crucibles  for  assay   of 
lead,  with  or  without  Up. — These  are  from  8  to  12  centimeters 
5 


Fig.  52. 


Fig.  53. 


Fig.  54. 


Fig.  55. 


6b  ASSAYING. 

high,  and  5  to  8  centimeters  wide.     The  sides  are  from  10  to  12 
millimeters   thick,  and    the   bottom   from    2   to   3   centimeters. 
Other  iron  vessels  used  are,  tubes  and  retorts,  and  cast-iron  muffles. 
C.  Vessels  of  bone-ash:  Cupels  (Fig.  54). — They  are  made  either 
of  bone-ash  alone,  or  with  an  addition  of  a  little  wood-ash,  or 
pearl-ash,  to  the  water  used  for  moistening  the  bone- 
ash,  which  addition  decreases  their  power  of  conduct- 
'fl.^f       ing  heat.     The  bones  are  burnt  white  throughout, 
^^^        are  then  powdered  and  washed.     The  dried  powder, 
which  should  be  about  as  fine  as  coarse  wheat  flour, 
is  used  for  the  principal  mass,  while  a  finer  flour  is  reserved  for 
a  final  coating.     The  cupels  are  formed  by  filling  and  driving 
the  prepared  bone-ash  into  a  mould  made  for  the  purpose  (Fig. 
55),  J5,  the  pestle;  A,  the  mould;  or  they 
are  pressed.1     Ordinary  Freiberg  cupels  for 
ores  consist  of  3  volumes  of  soap-boilers'  ash, 
and   1  volume  bone-ash.     Their  outer  di- 
ameter is  35  millimeters,  diameter  in  the 
clear  24  to  25  millimeters.     They  are  10  to 
12   millimeters   high   in   the  clear,  with  a 
total   height   of  18    millimeters.     Fine   or 
mint    cupels    consist    of    2    volumes    soap 
boilers'  ash,  and  3  volumes  bone-ash.    Their 
total  diameter  is  26  millimeters,  with  a  clear 
diameter    of    18    millimeters;    their    total 
height  is  14  millimeters.     Cupels  in  order 
to  be  perfect  should  dry  very  slowly,  and  be  thoroughly  ignited 
before  they  are  used.    They  should  be  white,  and,  besides  a  certain 
degree  of  solidity,  should  possess  the  requisite  porosity  to  absorb 
litharge  (when  taken  up  with  the  tongs  they  must  not  crumble, 
but  it  should  be  possible  to  crush  them  with  the  fingers).     They 
must  neither  undergo  any  perceptible  change  nor  crack,  when 
exposed  to  a  \vhite  heat,  and  should  develop  no  gases  and  form 
no  chemical  combinations  with   the  substance  fused    in  them. 
When  too  solid  they  crack  easily,  absorb  the  litharge  too  slowly, 
cupellation  being  thereby  prolonged,  which  causes  a  loss  of  silver. 


1  B.  u.  h.  Ztg.  1868,  p.  154. 


ASSAY   VESSELS    FOR   THE   DRY   METHOD. 


67 


If,  on  the  other  hand,  they  are  too  porous,  they  absorb  too 
much  silver  and  gold  with  the  lead  oxides.  (A  loss  of  metal 
can  never  be  entirely  avoided  in  the  assay.) 

Wait1  suggests  the  very  simple  machine  for  making  cupels  as  is 
shown  in  Fig.  56.     It  consists  of  a  common  letter-press,  the  mov- 

Fig.  56. 


able  platen  of  which  has  been  removed,  and  replaced  with  a  plunger, 
which  turns  with  the  screw,  moving  up  and  down,  and  making  the 
depression  in  the  cupel.  The  ring  holding  the  bone-ash  is  held  in 
place  directly  underneath  the  plunger  by  a  wooden  guide  fastened 
to  the  base  of  the  press.  There  is  also  fastened  to  the  top  of  the 
guide  for  the  ring,  at  a  distance  above  the  base  of  the  press  equal 
to  the  height  of  the  cupel-ring,  a  piece  of  wood  f  inch  thick, 
under  which  the  ring  will  just  slide  into  place,  and  through  which 
there  is  a  circular  hole  into  which  the  plunger  exactly  fits ;  this  last 

1  Note  on  a  cupel-machine.     Prof.  Charles  E.  Wait,  Trans.  Amer.  Institute 
of  Mining  Engineers,  vol.  xiv.  p  767. 


68  ASSAYING. 

guide  not  only  directs  the  plunger,  but  also  prevents  the  lifting  of 
the  ring  by  the  plunger.  There  is  also  a  small  spring  (not  shown 
in  the  figure)  which  pushes  forward  the  ring  after  the  ash  has  been 
compressed.  To  make  a  cupel,  fill  the  ring  with  slightly  moistened 
ash,  the  plunger  being  raised  just  high  enough  to  allow  the  ring  to 
be  put  in  place  with  the  left  hand,  with  the  right  hand  give  the 
wheel  about  one  turn,  depending  upon  the  pressure  required,  re- 
verse the  wheel  until  the  plunger  is  raised,  and  remove  the  thumb 
suddenly,  at  which  moment  the  spring  will  push  the  ring  to  the 
front.  Cupels  of  almost  any  size  may  be  made  by  having  plunger, 
ring,  and  guides  to  suit. 

D.  Vessels  of  other  materials. — Cupels  in  the  form  of  a  prism, 
about  2.5  centimeters  high  and  4  centimeters  thick,  are  chiselled 
out  of  charcoal,  or  turned  from  hard  wood  and  then  carbonized. 
Coke  cupels  are  made  of  powdered  and  sifted  coke,  which  is 
kneaded  with  liquid  pitch.  The  stiff  mixture  formed  after  the 
mass  has  become  cold,  is  pulverized,  and  some  more  powdered 
coke  added  to  it  (4  parts  of  coke  to  1  part  of  pitch).  The  entire 
mass  is  then  passed  through  a  hair  sieve,  heated,  and  stamped  in 
a  cupel-mould  about  2.5  centimeters  high,  with  a  diameter  of  3.7 
centimeters  von  the  top  and  3  centimeters  on  the  bottom.  The 
finished  cupels  are  then  ignited,  the  air  being  excluded  during 
the  operation. 

16.   ASSAY  VESSELS  FOR  THE  WET  METHOD. 

1.  For  assays  by  gravimetric  analysis. — Articles  of  glass:  di- 
gesting-flasks  or  matrasses,  beaker-glasses,  funnels,  watch-glasses, 
wash-bottles,  stirring-rods,  retorts,  tubes,  apparatus  for  generating 
sulphuretted  hydrogen,  etc.      Of  porcelain:  crucibles,  evaporating 
dishes,  tubes,  etc.     Of  other  materials:  forceps,  crucible  tongs, 
wire  triangles,  wire  gauze,  etc.1 

2.  For  assays  by  volumetric  analysis,  see  p.  40. 

3.  For  assays  by  colorimetric  analysis. — Tapering  glasses   or 

1  Muencke's  Klemmvorriclitung  in  Dingier,  ccxxv.  387.  Dreiecke  und 
Tiegelzangen  mit  Porzellanarmirung  in  Fresenius's  Ztsclir.  1879,  p.  259. 
Doppelaspirator,  Dingier,  ccxxv.  619. 


BALANCES — WEIGHTS.  69 

tubes  of  a  uniform  diameter  for  comparing  colors ;  graduated 
measuring  vessels  of  glass  or  porcelain,  divided  into  centimeters, 
ounces,  etc. ;  dissolving  vessels,  etc. 

V,  Balances  and  Weights, 

17.    BALANCES. 

Of  these  will  be  required — 

1.  An  ore  balance,  for  weighing  ores  and  the  regulus  of  base 
metals.     This   should   be  capable  of  carrying  from   30   to  50 
grammes,  and,  with  5  grammes  in  each  pan,  must  be  distinctly 
sensitive  to  an  addition  of  1  milligramme. 

2.  Bullion  or  button  balance,  inclosed  in  a  case,  for  weighing 
gold  and  silver  beads  and  alloys  of  precious  metals.     It  should 
be  capable  of  carrying  5  grammes  at  the  utmost,  and  must  dis- 
tinctly turn  with  -fa  to  -fa  milligramme  when   both  pans  are 
loaded  with  1  gramme. 

3.  An  apothecary  balance,  for  weighing  larger  quantities.     It 
should  be  sensitive  to  5  milligrammes. 

4.  A  rough  scale,  for  weighing  approximately  larger  quantities 
(fluxes,  etc.).     A  grocer's  scale  will  answer  the  purpose. 

18.  WEIGHTS. 

The  following  are  used  : — 

1.  The  gramme  weight,  from  50  to  0.001  gramme;  for  silver 
coins  from  1  gramme  =  1000  parts  to  y^Vo"  Par>t  '•>  for'assays  of 
gold  from  J  gramme  as  the  unit  =  1000  parts  to  j^Vrr  Part- 

2.  Centner. — 1  assay  centner  =  5  grammes  (Upper  Harz)  or 
=  3.75   grammes  (Freiberg)  =  100   pounds,  which   is   divided 
into  100  parts  of  pounds,  or  the  quint,  the  smallest  weight  being 
J  of  the  quint. 

In  Austrian  smelting  works,  etc.,  1  assay  centner  =10 
grammes,  which  is  divided  into  100  parts,  called  pounds;  the 
pound  is  divided  into  32  loth,  the  loth  into  4  quentchen,  and 
this  into  4  denar,  the  smallest  weight  being  1  denar=0.195 
milligramme. — English  grain  weight.  The  unit  is  usually  1000 


70  ASSAYING. 

grains.  The  smallest  weight  for  gold  and  silver  buttons  is  0.001 
grain.  For  an  assay  of  ore,  generally  a  sample  is  taken  weigh- 
ing 400  grains.  The  divisions  of  this  system  are  as  follows  :  1 
ounce  =s  480  grains  =  20  pennyweights  (24  grains  to  the  penny- 
weight).— American  assay  weight.  1  assay  ton  =  29.166  grammes 
(450.26  grains) ;  1  pound  avoirdupois  (commercial  weight)  = 
7000  troy  grains  (apothecaries7  weight) ;  1  ton  =  2000  pounds 
avoirdupois;  2000  X  7000=14,000,000  grains  troy  in  1  ton 
avoirdupois;  480  grains  troy  =  1  ounce  troy;  14,000,000-^-480 
=  29,166  troy  ounces  in  2000  pounds  avoirdupois ;  one  assay  ton 
contains  29,166  milligrammes,  therefore,  2000  pounds  are  to  1 
assay  ton  as  1  ounce  troy  weight  to  1  milligramme.  If,  for 
instance,  an  assay  ton  yields  1  milligramme  of  gold  or  silver  the 
result  will  be  1  ounce  troy  in  2000  pounds  avoirdupois  without 
further  calculation.1 

VI.  Tools  and  Implements. 

19.    GENERAL  REMARKS. 

We  will  only  consider  the  tools  and  implements  required  for 
the  dry  method,  as  those  for  the  wet  method2  do  not  diifer  from 
those  used  in  analytical  chemistry  (stands,  forceps,  crucible 
tongs,  cork  drill,  etc.). 

20.    FURNACE  TOOLS. 

The  following  tools  are  used  in  attending  the  furnaces. 
Shovels  with  perforated  blades  for  handling  the  fuel ;  large  and 
small  iron  pokers  and  scrapers  for  cleansing  the  grate  and  muffle, 
poking  the  coal,  etc. ;  coal  and  ash  sieves  with  meshes  respectively 
1  centimeter  and  3  millimeters  wide ;  iron  boxes  filled  with  water 
for  cooling  the  tools,  etc. 

1  For  general  practice  it  is  far  preferable  to  use  the  French  metric  system 
of  weights,  instead  of  the  arbitrary  and  varying  German  systems.     The  sim- 
plicity and  convenience  of  the  American  assay  ton  leave  nothing  to  be  de- 
sired.— TRANSLATOR. 

2  Neuere  Gerathschaften  in  Fresenius's  Ztschr.  f.  anlyt.  Chemie. 


IMPLEMENTS.  71 

21.    IMPLEMENTS. 

The  following  are  required  : — 

A.  For  preparing  the  assay  sample. 

1.  Sampling. — Iron  spoom  having  a  diameter  of  4  centimeters ; 
shovels ;  troughs,  wooden  boxes,  etc.,  for  the  reception  of  the  assay 
samples ;  files  and  cold  chisels  ;  hollow  chisels  ;  drills  ;  hollow  cylin- 
ders of  sheet  iron  for  small  ore ;  magnifying  glass,  etc. 

2.  For  drying  the  samples  (p.  24). — Drying  pans  of  sheet  iron 
or  copper ;  drying  frames  ;  iron  spatulas  ;  drying  disk  (Fig.  2,  p. 
25);  water-baths  (Fig.  1,  p.  24);  air-baths;  desiccators  (Fig.  19, 
p.  40),  etc. 

3.  For  comminuting  the  samples  (p.  25). — Grinding  plate  and 
rubber;  mortars;  hammers;   anvils;   rolls;  common  scissors  and 
plate  shears;  files;  rasps;  pliers;  vise,  etc. 

4.  For  sifting. — A  series  of  sieves  of  from  20  to  100  meshes  to 
the  inch,  for  sifting  ores,  fluxes,  etc.     A  box  sieve,  consisting  of 
a  round  tin  box,  into  which  a  sieve  can  be  snugly  fitted,  is  very 
useful,  as  in  sieving  the  pulverized  ore  there  is  no  dust.     If 
desired,  a  tin  cover  can  be  made  to  inclose  the  whole. 

5.  For  ivashing   (p.   27). — Beaker  glasses;    glass   cylinders ; 
iron  vanning  shovels  (Fig.  5,  p.  27),  etc. 

6.  For  weighing. — Brass  pincettes  with  fine  ivory  points  for 
taking  up  small  weights,  metal  buttons,  etc.,  and  others  with 
blunt  or  broad  points  for   lifting   larger  weights  and   heavier 
buttons  of  precious  and  base  metals;   brass  mixing  spoons,  18 
centimeters  long  and  2  centimeters  wide,  having  on  one  end  a 
spatula  1.2  centimeters  wide;   camel's  hair  and  bristle  brushes; 
watch-crystals;   small  glass  or  porcelain  vessels;  glass  tubes,  one 
end  fused  shut  and  the  other  closed  with  a  cork  or  glass  stopper ; 
glazed  paper;   artistically  closed  cornets  of  fine  letter  paper  of 
diiferent  colors.     They  are  used  for  the  reception  of  shavings, 
granules,  etc.,  of  alloys,  etc. 

7.  For  charging. — Mixing  scoops  (Figs.  6  and  7,  p.  30) ;  mix- 
ing spatula  of  brass  or  horn ;   bristle  brushes;  measuring  spoon 
for  granulated  lead :  touch  stones  and  touch  needles,  etc. 


72 


ASSAYING. 


B.  Implements  for  transporting  the  assaying  vessels  and  for 
manipulating  the  same  in  the  furnace. — Iron  tongs  (Fig.  57)  for 
catching  hold  of  the  vessels.  For  large  muffle-furnaces  they  are 


Fig.  57. 


Fig.  58. 


Fig.  59. 


Fig.  60. 


Fig.  61. 


80  to  100  centimeters  long,  and,  for  smaller  furnaces,  50  to  60 
centimeters.  Scorification  tongs  with  one  arm  forked,  as  shown 
in  Fig.  58,  the  horse-shoe  part  just  large  enough  to  fit 
the  scorifier,  60  millimeters  long  and  45  millimeters 
wide ;  crucible  tongs  (Fig.  60)  for  wind  and  blast  fur- 
naces. Small  assay  plates  of  sheet-iron,  with  handles. 
They  are  about  14  centimeters  square,  and  are  provided 
with  9  depressions,  each  28  millimeters  wide,  in  which 
cornets,  simple  weights  of  lead  (Bleischweren),  etc., 
are  kept.  The  following  implements  are  required  for 
manipulations  in  the  furnace  during  roasting,  fusing, 
etc. :  curved  stirring  rods  and  spatulas  of  iron ;  iron 
ladles;  tongs  with  curved  tips  (Fig.  59)  for  taking 
hold  of  cornets,  buttons,  etc. ;  cooling  iron  (Fig.  61). 
The  blade  of  this  for  large  muffle-furnaces  is  9  centi- 
meters long,  7  centimeters  wide,  and  1  centimeter  thick. 
It  is  provided  with  a  handle  85  centimeters  long.  For  small 
furnaces  the  respective  dimensions  are :  5  centimeters,  4  centi- 
meters, 0.7  centimeter,  and  70  centimeters. 


IMPLEMENTS. 


73 


Perhaps  the  best  tongs  for  all  around  work  are  the  kind  shown 
in  Fig.  62.     They  are  about  from  1J  to  2  feet  (4.5  to  6  decimeters) 
long  and  have  the  joint  about  3  inches  (7.6  centimeters) 
from  the  end.  F[S-  62- 

Figs.  63  and  64  show  respectively  Judson's  patent 
steel  scorification  and  cupel  tongs,  designed  to  enable 
the  operator  to  remove  the  scorifiers  or  cupels  from  the 
rear  of  muffle  without  disturbing  those  in  front. 

C.  Implements  required  for  the  reception  and  further 
treatment  of  the  assay  samples  after  they  have  been  taken 
from  the  furnace. 

1.  For  the  reception  of  the  assay  samples  are  required : 
sheet-iron  plates  with  handles.  They  are  divided  into 
squares  by  strips  of  sheet  iron  crossing  each  other,  or 
have  depressions,  each  about  4  centimeters  wide,  in 
which  the  assay  vessels  are  placed ;  open  and  closed 
ingot  moulds  for  casting  lead  and  silver  bars,  ingots,  etc. ;  small 
iron  or  leaden  plates  (Kornbleche),  about  10  centimeters  long  and 

Fig.  63. 


Pig.  64. 


60  millimeters  wide,  with  depressions  3  centimeters  wjde  for  the 
reception  of  gold  and  silver  buttons  from  the  cupel ;  and  boards 
of  wood  with  larger  depressions  for  the  reception  of  buttons  of 
base  metals. 

2.  For  the  further  treatment  of  the  samples  after  they  have  become 
cold. —  Hammers  for  breaking  the  clay  crucibles,  etc.,  and  re- 
moving the  slag  from  the  buttons.  The  body  of  these  is  about 


74  ASSAYING. 

9  centimeters  long,  the  head  square,  the  other  end  running  into 
a  point  (also  smaller  hammers) ;  an  anvil  with  a  plate  beneath  it 
about  6  centimeters  square;  cupel  tongs  (pliers),  160  centimeters 
long,  for  taking  the  buttons  of  silver  and  gold  from  the  cupels ; 
a  button  brush  consisting  of  a  brass  holder  with  bristles  at  both 
ends ;  a  bar  magnet  for  extracting  particles  of  iron  from  the  slag, 
etc. 

VII,  Assay  Reagents, 

22.    REAGENTS1   FOR   DRY   ASSAYS. 

According  to  their  action  they  may  be  divided  into — 
1.  Reducing  agents. — Charcoal  in  the  form  of  powder,  or  of 
small  pieces  placed  on  top  of  the  charge  (assays  of  lead,  copper, 
etc.),  or  of  crucible  lining  (assays  of  iron) ;  when  it  is  generally 
mixed  with  other  reducing  agents  (potassium  carbonate,  sodium 
carbonate,  etc.),  because  the  presence  of  a  large  percentage   of 
charcoal   without   additions   in   smelting   processes  renders   the 
charge  more  difficult  to  fuse. 

Powdered  coke,  anthracite,  and  graphite2  may  also  be  used  in- 
stead of  powdered  charcoal,  but  they  are  less  combustible.  Rosin, 
fat  oils,  tallow,  sugar,  etc.,  were  formerly  also  employed.  Bitar- 
trate3  of  potassium  (argol)  (KC4HSO6),  either  crude  or  refined, 
yields  considerable  carbon  in  becoming  carbonized,  and  in  con- 
sequence exerts  a  vigorous  reducing  effect,  but  causes  refractori- 
ness. For  this  reason  its  percentage  of  carbon  is  reduced,  if 
necessary,  by  mixing  it  in  different  proportions  with  saltpetre. 
The  mixture  is  poured  into  a  red-hot  crucible,  placed  under  a 
well-drawing  chimney.  The  mixture  deflagrates  and  emits  em- 
pyreumatic  vapors,  when,  by  reason  of  a  partial  oxidation  of  the 
carbon,  a  mixture  of  potassium  carbonate  and  carbon  is  formed. 
This  is  known  as  black  flux.  For  vigorous  reduction  it  is  made 
from  1  part  of  saltpetre  and  3  parts  of  argol ;  for  less  vigorous, 
either  of  1  and  2J,  or  1  and  2  parts  respectively.  Another  flux 

1  Muspratt's  techn.  Chemie,  3d  Aufl.     Bolley,   Handb.  der   teclm.   chem. 
Untersuchungen,  1879. 

2  Werthbestimmung  in  Fresenius's  Ztschr.  1875,  p.  394. 
8  Werthbestimmung  in  Fresenius's  Ztschr.  vii.  149. 


REAGENTS  -FOR   DRY   ASSAYS.  75 

containing  potassium  carbonate  (without  carbon),  mostly  with 
undecomposed  saltpetre,  and  known  as  white  flux,  consists  of 
1  to  2  parts  of  saltpetre,  and  1  part  of  argol ;  gray  flux  has  3 
of  argol  to  2  of  saltpetre.  A  mixture  of  argol  and  saltpetre, 
before  it  is  deflagrated,  is  called  raw  flux.  As  black  flux,  on 
account  of  its  hygroscopic  properties,  must  be  frequently  pre- 
pared fresh,  and  this  work  is  unpleasant  by  reason  of  the  evolu- 
tion of  bad  odors,  a  mixture  of  potassium  carbonate  (or  soda)  and 
flour  (starch  =  C6H]0O5),  which  is  also  cheaper,  is  used  in  prefer- 
ence. Uusually  20  to  25  per  cent,  of  wheat  flour  is  taken,  but 
for  more  vigorous  reductions  30  to  35  per  cent,  (for  instance  in 
assays  of  copper),  and  even  as  much  as  50  per  cent,  (assay  of 
tin).  When  this  mixture  is  used,  a  separation  of  carbon,  in  a 
fine  state  of  division,  takes  place,  with  the  exhibition  of  a  yellow 
flame  of  carburetted  hydrogen,  caused  by  the  carbonization  of 
the  flour  during  the  fusing  of  the  assay  sample.  The  flame  of 
the  carburetted  hydrogen  must  not  be  confounded  with  the  blue 
flame  of  carbonic  oxide.  Mixtures  of  potassium  carbonate  (or 
of  sodium  carbonate)  and  coal-dust  are  less  intimate,  and  their 
action  is  consequently  less  energetic  than  that  of  mixtures  in 
which  the  carbon  has  been  separated  from  organic  substances  in 
a  very  finely  divided  condition  (tartaric  acid,  flour).  Potassium 
cyanide,  with  64.1  K  and  35.9  Cy,  is  an  energetic  reducing  (also 
desulphurizing)  agent,  even  at  a  low  temperature  (assays  of  tin). 
Potassium  ferrocyanide,  K4Fe(CN)6,  yields,  on  heating,  a  mixture 
of  iron  carbide,  ferrous  and  ferric  oxides,  free  carbon,  and  a  small 
quantity  of  potassium  cyanide.  It  has  also  a  vigorous  desulphur- 
izing action. 

The  reducing  power  is  estimated  from  the  quantity  of  lead 
which  is  yielded  by  fusing  1  to  2  grammes  of  the  reagent  with 
60  grammes  of  litharge  and  15  grammes  of  sodium  carbonate  or 
potassium  carbonate. 

According  to  Berthier,  the  reducing  power  of  the  various  agents 
is  as  follows :  1  part  hydrogen,  104 ;  pure  carbon,  34.31 ;  well- 
glowed  wood  charcoal,  31.81;  ordinary  wood  charcoal,  28.00; 
tallow,  15;  sugar,  14.5;  kiln-dried  starch,  13;  ordinary  starch, 
11;  tartaric  acid,  6;  oxalic  acid,  0.90;  black  flux  with  2  parts 
of  argol,  1.40;  black  flux  with  2J  parts  of  argol,  1.90;  black 


76  ASSAYING. 

flux  with  3  parts  of  argol,  3.80;  94  parts  soda  and  6  wood  char- 
coal, 1.80 ;  88  parts  soda  with  12  charcoal,  3.60;  90  parts  of  soda 
with  10  of  sugar,  1.40;  90  parts  of  soda  with  10  of  starch,  1.15; 
80  parts  of  soda  with  20  parts  of  starch,  2.30 ;  crude  argol,  5.60 ; 
purified  argol,  4.50;  pure  argol  (carbonized),  3.10;  potassium 
binoxalate  (salt  of  sorrel),  0.90;  white  soda-soap,  16  parts. 

2.  Oxidizing  agents. — Saltpetre,  KNO3,  with  46.56  K2O,  and 
53.44  N2O5.  It  should  be  as  free  from  sulphates  as  possible. — 
Litharge,  PbO,  with  92.83  Pb,  and  7.17  O,  exerts  an  oxidizing 
eifect  upon  metals  and  metallic  sulphides  (scorification),  as  well 
as  upon  organic  substances  (assay  of  fuel).  As  generally  used  it 
is  in  the  form  of  red  litharge  free  from  particles  of  metallic  lead.1 
It  should  completely  dissolve  in  acetic  acid,  and  be  as  free  from 
gold  and  silver  as  possible.  When  it  contains  silver,  white  lead 
not  adulterated  with  heavy  spar,  2  (PbCO3)  +  Pb(HO)2,  with 
86.27  PbO,  may  be  substituted  for  it.  It  is  best  to  prepare  this 
by  the  wet  method  (for  instance,  by  that  of  Dietel,  of  Eisenach, 
which  yields  a  product  from  gold,  silver,  antimony,  and  copper). 

According  to  Berthier,  1  part  of  the  various  metallic  sulphides 
requires  the  following  quantities  of  litharge  for  its  decomposi- 
tion : — 

Parts. 

PbS 1.87 

Hgs ...     10  to  12 


BiS  .         . 

Sb2S3  .         . 

ZnS 

FeS 

SnS2  . 

Copper  pyrites 

FeS2  . 

As2S3  . 


.     20 

.     25 

.     25 

.     30 

25  to  30 

30  to  35 

\     50 

50  to  60 


Litharge  entirely  free  from  silver  can  be  prepared  by  oxidizing 
the  purest  Pattison  or  Villaeh  lead  by  cupellatiori,  or  bringing 
such  lead,  after  it  has  been  granulated,  into  fused  saltpetre ;  or 
by  gradually  strewing  charcoal  powder  upon  litharge  fused  in 
refractory  crucible,  whereby  some  lead  will  be  reduced  which,  in 
sinking  down,  withdraws  the  silver  from  the  litharge. 

1  Dingier,  cxciv.  84. 


REAGENTS   FOR   DRY   ASSAYS.  77 

3.  Solvent  agents. 

a.  Acid  ;  such  as  powdered  quartz  ;  powdered  glass1  free  from 
arsenic  and  lead.     It  should  contain  60  to  70  per  cent,  or  more 
of  SiO2,  5  to  22  per  cent,  of  alkalies,  6  to  25  per.  cent,  of  lime, 
0.5  to  5  per  cent,  alumina,  and  its  fusing  point  should  be  be- 
tween that  of  borax  and  fluor-spar,  or  about  1200°  C.  (2192°  F.). 
Borax,  NaaB4O7  +  10  H2O,  with  16.37  Na2O,  36.53  BO3,  and 
47.10  H2O.     It  should  be  completely  dehydrated,  or  in  the  con- 
dition known  as  borax-glass.     This  is  produced  by  fusing  borax 
in  a  clay  crucible,  and  then  pouring  it  upon  a  bright  metallic 
surface.     It  is  more  fusible  than  glass,  and  the  boracic  acid  forms 
combinations  with  nearly  all  the  bases  as  well  as  with  silicic 
acid.     Salt  of  phosphorus  (sodium-ammonium-hydrogen  phosphate), 
or  microcosmic  salt,  NaH(NH4)P  +  4H2O,   with    14.90   Na2O, 
12.46  NH4O,  4.29  basic  water,  and  34.32  water  of  crystallization, 
and  34.03  P2O5.     In  the  anhydrous  condition  it  is  a  more  ener- 
getic solvent  agent  than  borax  (assays  of  cupreous  nickel).     Clay, 
such  as  kaolin,  Al2Si2O7,  with  46.40  SiO2,  39.68  A12O3,  6.96  H2O 
and  6.96  ag. ;  burned  China  clay  contains  53  Si2O2  and  47A12O3. 
Most  varieties  of  clay  contain  over  50  per  cent,  of  silicic  acid. 

b.  Basic;    such  as  potassium  carbonate,  K2CO3,  with  68.09 
K2O  and  31.91  CO2.     It  should  be  as  free  as  possible  from  sul- 
phates, and  when  mixed  with  carbon  as  black  flux  (p.  74),  and 
with  flour  (p.  75),  is  a  vigorous  reducing,  fluxing,  and  desulphu- 
rizing agent.     Sodium  carbonate,  Na2CO3,  with  58.58  Na2O  and 
41.42  CO2,  acts  somewhat  less  energetically  than  potassium  car- 
bonate, and  consequently  a  larger  quantity  of  it  must  be  used.    It 
is  less  deliquescent,  more  fusible,  and  cheaper.     A  mixture  of  13 
parts  of  dry  potassium  carbonate  and  10  parts  of  calcined  sodium 
carbonate,  furnishes  a  flux  very  easily  fusible. — Caustic  alkalies 
act  more  energetically  than  carbonates,  but  exert  a  very  injurious 
effect  upon  the  crucibles. — Calcium  carbonate,  CaCO3,  with  56.29 
CaO,  in  the  form  of  chalk  (or  calcite),  may  be  used  for  smelting 
operations  at  higher  temperatures  (for  instance,  in  assays  of  iron, 
Cornish  assays  of  copper). — Fluor-spar  (calcium  fluoride),  CaFl2, 

1  Analyses  of  Glass,  in  Poggendorf  s  Ann.  1879,  vol.  6,  p.  431.     Dingier, 
ccxxxii.  348  (Weber). 


78  ASSAYING. 

with  51.54  Ca,  is  more  easily  fusible  than  calcium  carbonate,  and 
is  especially  effective  for  removing  silicic  acid.  It  readily  fuses 
down  with  calcium  phosphate,  heavy  spar,  and  gypsum. — Lead 
oxide  (litharge,  minium,  white  lead)  readily  fuses  with  silicic 
acid,  the  alkalies,  and  with  most  of  the  heavy  metallic  oxides, 
but  less  so  with  the  earths  and  alkaline  earths. — Ferric  oxide, 
F2O3,  with  69.3  Fe  (in  assays  of  copper). 

4.  Precipitating  or  desulphurizing  agents. — Iron  in  the  form  of 
iron  filings  (assays  of  zinc  blende,  antimony,  and  mercury),  and 
as  pieces  of  wire  4  to  5  millimeters  thick,  6  to  9  millimeters 
long,  and  weighing  from  0.5  to  2  grammes  (assays  of  lead  and 
bismuth). — Potassium  cyanide  (p.  75)  and  potassium  ferrocyanide 
(p.  75).     The  caustic  alkalies  and  carbonates  (p.  77)  decompose 
metallic  sulphides.     The  metal  is  separated,  and  sulphites,  hypo- 
sulphites, and  sulphates  of  the  alkalies  together  with  alkaline  sul- 
phide are  formed.     The  latter  forms  a  sulpho-salt  (for  instance, 
with  FeS,  PbS,  and  Cu2S)  with  one  part  of  the  metallic  sulphide, 
which,  as  a  general  rule,  can  be  decomposed  with  iron.     Carbon 
promotes   desulphuration  (black  flux,  potassium  carbonate,  and 
flour,  pp.  74,  75). — Lead  oxide  (p.  76). — Saltpetre  oxidizes  metallic 
sulphides,  while  the  metals  (silver,  copper,  lead)  are  separated. 

5.  Sulphurizing  agents. — Sulphur  in  the  form  of  flowers  of 
sulphur ;  or  of  iron  pyrites  (Cornish  assay  of  copper). 

6.  Concentrating  fluxes. — Lead  in  a  granulated  condition  (assay 
lead).    It  is  prepared  by  rocking  lead  in  the  form  of  thick  liquid 
paste  in  a  trough  well  covered  with  chalk  and  then  sifting  the 
mass.     It  is  also  used  in  the  form  of  sticks  of  the  purest  Pattison 
lead  for  alloying  with  gold  and  silver.     (Where  the  assayer  is 
obliged  to  make  his  own  granulated  lead,  as  in  sections  where 
pure  lead  free  from  silver  cannot  be  obtained,  it  will  be  necessary 
for  him,  after  granulation   in  the  manner  above  described,  to 
sample  well,  and  test  about  30  to  50  grammes  for  silver  by  the 
scorification  assay.      In  using  this  lead,  the  amount  of  silver 
contained  in  it  must,  in  all  cases,  be  deducted  from  the  results 
obtained  in  making  an  assay.) — Silver*  for  alloying  with  gold 

Preparation  of  pure  silver:  Cupriferous  silver  or  fine  silver  is  dissolved  in  pure 
nitric  acid.  This  is  diluted  with  distilled  water,  allowed  to  stand  for  some 
time,  and  then  filtered.  The  filtrate  is  strongly  diluted,  and  chloride  of  silver 


REAGENTS   FOR   DRY   ASSAYS.  79 

(quartation). —  Gold  for  collecting  copper  (assay  of  nickel  and 
cobalt). — Antimony  (antimony  oxide)  and  arsenic  for  copper  (re- 
fining).— Copper  oxide  for  tin. — Iron  pyrites  as  a  collecting  agent 
for  copper  (assay  of  matt). 

7.  Decomposing  and  volatilizing  fluxes. —  Charcoal  and  graphite 
for  decomposing  sulphates,  arseniates,  and  antimoniates  by  roast- 
ing.— Ammonium    carbonate   (NH4)3CO3   for   decomposing    sul- 
phates, especially  copper  sulphate,  at  red  heat  (p.  33),  but  less 
completely  lead  and   bismuth   sulphates. — Common  salt  (sodium 
chloride)  NaCl,  with  39.66  Na  and  60.34  Cl,  for  the  volatiliza- 
tion of  antimony  and  arsenic  in  refining  black  copper  according 
to  the  Cornish  method. 

8.  Air-excluding  fluxes  (covering  agents). — Decrepitated  common 
salt,  as  free  from  sulphates  as  possible,  fuses  easily,  and,  becoming 
very  thin  fluid,  washes  down  particles  of  metal  adhering  to  the 
sides  of  the  assay  vessels.     It  volatilizes  at  a  red  heat. —  Glass 
(p.  76)  in  Berthier's  assay  of  fuel  and  assay  of  matt. — Refined 
slag  from  charcoal  iron  blast-furnaces  (in  assays  of  zinc). 

is  precipitated  by  the  addition  of  pure  hydrochloric  acid.  This  is  washed  by 
decantation  and  then  boiled  several  times  with  diluted  hydrochloric  acid,  but 
after  each  boiling  it  should  be  washed  with  distilled  water.  The  moist  chlo- 
ride of  silver  (3  parts)  is  mixed  with  dry  sodium  carbonate  (1£  parts)  and 
with  pure  saltpetre  (£  part  of  the  whole).  The  mixture  is  then  dried  in  a 
porcelain  dish  and  fused  in  a  porcelain  crucible  ;  or  100  parts  of  chloride  of 
silver  are  fused  with  70  parts  of  chalk,  and  4  parts  of  wood  charcoal.  (Mohr, 
Titrirmethode,  1874,  p.  425.  Fresenius's  Ztschr.  xiii.  179.) 

[Star  recommends  the  following  process  as  yielding  a  metal  which  comes 
nearer  ideal  purity:  Slightly  cupriferous  silver  is  converted  into  dry  nitrate, 
and  fused  to  reduce  any  platinum  nitrate  present  to  metal.  The  fused  mass 
is  taken  up  with  dilute  ammonia  and  then  diluted  to  about  fifty  times  the 
weight  of  silver  it  contains.  The  filtered  solution  is  now  mixed  with  an 
excess  of  a  sulphide  of  ammonia  solution,  S03(NH4)2,  and  allowed  to  stand. 
After  twenty-four  hours,  about  half  of  the  silver  has  separated  out  in  crystals ; 
from  the  mother  liquor  the  rest  comes  down  promptly  on  the  application  of  a 
water-bath  heat.  The  rationale  of  the  process  is  that  the  sulphide  hardly 
acts  upon  the  dissolved  oxide  of  silver,  but  it  reduces  some  of  the  oxide  of 
copper,  2CuO,  to  Cu20,  with  the  formation  of  sulphate  S04(NH4)2.  This  Cu2O 
dioxidizes  its  equivalent  of  Ag2O,  forming  Ag+  Cu202,  which  latter  is  reduced 
by  the  stock  sulphide  and  reconverted  into  Cu20,  which  now  acts  upon  a  fresh 
equivalent  of  Ag20;  and  so  on  to  the  end. — GL] 


80  ASSAYING. 


23.    REAGENTS   FOR   WET   ASSAYS. 

The  following  are  principally  used  : — 

1.  For  assays  by  gravimetric  and  colorimetric  analysis. — Acids: 
hydrochloric,  sulphuric,  nitric,  and  acetic  acid,  aqua  regia  (nitro- 
muriatic  acid).    Bases  and  salts:  caustic  alkalies,  alkaline  carbo- 
nates, potassium  chlorate,  ferrous  sulphate,  sodium  sulphide,  etc. 
— Metals  for  precipitation  :  iron  in  the  form  of  wire-pins  30  to  35 
millimeters  long  and  2  to  3  millimeters  thick,  or  in  a  pulverulent 
condition,  for  copper ;  zinc  in  the  form  of  such  pins  or  of  gran- 
ules,1 or  in  a  pulverulent  state,2  as  a  reducing  agent  for  iron  solu- 
tions,  etc.  ;  copper  (electrolytic  copper  is  the  purest) ;  bromine* 
for  decomposing  sulphurets,  compounds  of  gold,  etc. 

2.  For  volumetric  assays :   Potassium  permanganate  (chame- 
leon), KMnO4,  with  29.8  K2O  and  70.2  Mn2O7 ;  sodium  sulphide  ; 
potassium  cyanide  ;  barium  chloride ;  potassium  iodide ;  free  and 
with  dissolved  iodine ;  sodium  hyposulphite ;  ferric  chloride ;  so- 
dium chloride  ;  potassium  sulphocyanide,  etc.     As  indicators  :  lit- 
mus tincture,  tincture  of  Brazil  wood*  etc.,  for  acids  and  alkalies  ; 
for  sulphur :  the  salts  of  iron,  nickel^  and  lead,  and  sodium  nitro- 
prusside ;    for  iodine:  starch  paste;   for  iron  oxide:  potassium 
sulphocyanide,  etc. 

1  [Zinc  is  very  easily  granulated  by  pouring  the  molten  metal  into  a  bucket 
of  warm  water. — G.] 

2  Dingier,  ccxxviii.  378.  3  Dingier,  ccxix.  544. 

4  Fresenius's  Ztschr.  1875,  p.  324  (Rothliolz).     Bericlit  der  deutsch.  chem. 
Ges.  1877,  p.  1572  (Fluorescein). 


SPECIAL  DIVISION. 


I,  LEAD, 

24.    LEAD  OEES. 

Galena  (lead  monosulphide)  PbS,  with  86.6  Pb ;  cerusite  (lead 
carbonate)  PbCO3,  with  76.6  Pb  ;  anglesite  (lead  sulphate)  PbSO4, 
with  68.3  Pb ;  pyromorphite  3Pb3P2O8  +  PbCl,  with  76.3  Pb ; 
crocoisite  (lead  chromate)  PbCrO4,  with  63.2  Pb ;  wulfenite  (mo~ 
lybdate  of  lead)  PbMoO4,  with  57  Pb. 

25.    ASSAYS   OF   LEAD  IN  THE  DRY  WAY. 

The  results  of  these  assays  are  inaccurate,  as  the  lead  is  liable  to 
slag  off  and  to  volatilize,  which  is  promoted  by  the  presence  of 
other  volatile  substances  (arsenic,  zinc,  antimony),  and  also  by 
reason  of  a  possible  contamination  of  the  lead  by  other  metals 
(copper,  arsenic,  antimony,  bismuth).  The  highest  yield  which 
can  be  obtained  from  pure  galena  is  85.25  per  cent.,  but  in  poorer 
ores  the  loss  of  lead  may  be  5  per  cent,  greater.  The  results  are 
sometimes  calculated  to  whole  per  cents.,  but  more  frequently 
from  5  to  5  per  cent. 

The  condition  of  the  ore,  whether  the  lead  is  sulphurized  or 
oxidized,  and  whether  the  substance  is  pure  or  contains  more  or 
less  of  earths  and  foreign  metallic  sulphide,  will  decide  the  choice 
of  the  assay  method. 

I.  Sulphurized  Substances. 

A.   Galena,  etc.,  without  foreign  metallic  sulphides  (ZnS,  FeS, 
Cu2S,   Sb2S3,  As2S3). — Precipitation  assay:  the  assay  sample  is 
either  decomposed  by  alkalies  alone  (Upper  Harz  assay  with 
6 


82  ASSAYING. 

potassium  carbonate,  assay  with  potassium  cyanide),  or  together 
with  metallic  iron  (in  an  iron  pot  or  clay  crucible),  with  the  fol- 
lowing reactions : — 

The  lead  sulphide  is  decomposed  by  the  alkalies  at  a  compara- 
tively low  temperature  (7  PbS  +  4K2CO3  =  4Pb  +  3(K2PbS2) 
+  K2SO4  +  4CO2).  The  sulpho-salt  (K2PbS2),  which  otherwise 
would  pass  into  the  slag,  is  either  decomposed  by  iron  at  a  high 
temperature,  3(K2PbS2)  +  3Fe  =  3Pb  +  3(K2FeS2,)  or,  as  is 
the  case  in  the  Upper  Harz  assay  with  potash,  by  a  suitable  ad- 
mission of  air  at  a  lower  temperature.  By  this  process  the  K2S 
of  the  sulpho-salt  is  completely  converted  into  K2SO4,  but  the 
PbS  only  partly  into  PbSO4,  so  that,  by  increasing  the  heat,  the 
still  remaining  PbS  is  decomposed  by  the  PbSO4,  as  follows : 
(PbS  -f  PbSO4  =  2Pb  +  2SO2.)  In  the  first  case,  the  presence 
of  carbon  (black  flux,  flour,  tartaric  acid,  etc.)  promotes  desulphu- 
rization. 

1.  Rich  galena  (with  little  earths). 

a.  Assay  in  an  iron,  pot  (Belgian  assay}. — This  is  the  best 
method  of  assaying  lead,  as  pure  galena  with  86.6  Pb  yields  84.25 
to  85.25  per  cent,  of  lead,  therefore,  with  a  loss  of  but  1  to  2  per 
cent,  and  sometimes  only  0.5  per  cent,  of  lead.  It  also  permits 
the  use  of  a  larger  charge,  and,  the  iron  pot  being  a  good  con- 
ductor of  heat,  the  operation  can  be  more  quickly  executed  and 
at  a  comparatively  low  temperature.  When  large  quantities  of 
earth  are  present,  more  slag  will  be  formed,  and  consequently  the 
resulting  loss  of  lead  will  increase,  according  to  Percy,1  at  the 
following  rate  :  1.80  to  7.90  per  cent,  when  the  ore  contains  from 
10  to  90  per  cent,  of  calcium  carbonate,  and  1.18  to  35  per  cent, 
when  10  to  90  per  cent,  of  silicic  acid  is  present.  The  sample  is 
less  frequently  fused  without  any  fluxes  (Flintshire)  than  with 
alkaline  fluxes.  An  addition  of  carbon  (black  flux,  flour,  argol) 
checks  the  oxidation  of  the  lead,  promotes  the  reduction  of  the 
lead  carbonate  and  lead  sulphate  which  may  be  present,  and  pre- 
vents the  oxidation  of  the  iron  sulphide.  The  latter  (oxide  of 
iron)  vigorously  attacks  the  walls  of  the  pot  and  retains  particles 

1  [Metallurgy  of  Lead.  By  John  Percy.  London  :  John  Murray,  1870,  pp. 
113-117.— G.] 


ASSAYS   OF   LEAD   IN   THE   DRY   WAY.  83 

of  lead  when  the  contents  of  the  pot  are  poured  out.  Fluor- 
spar is  a  good  flux  for  heavy  spar.  Silver  and  gold  pass  entirely 
into  the  lead,  but  only  traces  of  zinc  and  iron.  Copper  divides 
itself  between  lead  and  slag.  A  large  part  of  the  antimony 
passes  into  the  lead,  and  while  a  part  of  the  arsenic  volatilizes, 
very  little  of  it  passes  into  the  lead,  and  the  largest  part  forms 
spiess  with  iron. 

Fifty  grammes  of  ore  are  placed  in  an  iron  pot  previously  heated 
to  dark  redness,  in  a  coke  fire  in  the  wind-furnace,  or  in  a  gas- 
furnace.  From  50  to  100  grammes  of  black  flux  or  potassium 
carbonate  with  15  to  20  per  cent,  of  flour  are  added,  then  2  to  % 
grammes  of  borax,  and  finally  a  covering  of  common  salt  5  milli- 
meters thick.  The  charged  crucible  is  then  placed  between  the 
darkly  glowing  coal  in  the  furnace.  The  latter  is  closed,  and  the 
temperature  gradually  raised  in  about  five  minutes  to  complete 
redness,  and  this  is  kept  up  until  the  contents  of  the  crucible  are 
in  quiet  fusion  without  foaming  (three  to  five  minutes).  The 
granules  of  lead  floating  on  the  top  should  be  submerged  by 
means  of  an  iron  spatula  or  wooden  rod.  The  furnace  is  then 
closed  for  a  few  minutes,  after  which  the  pot  is  taken  out  and 
allowed  to  cool  oif  somewhat.  Its  contents  are  poured  into  a 
mould,  which  should  have  been  previously  coated  with  graphite 
and  heated.  If  the  contents  are  poured  out  while  too  hot,  a  film 
of  lead  may  remain  adhering  to  the  iron,  and,  if  too  cold,  the 
lead  will  partly  spread  over  the  slag.  The  mould,  after  having 
been  allowed  to  cool  off,  is  turned  over,  and  the  hard,  black  slag 
is  quickly  broken  off  from  the  lead  button  to  prevent  it  from 
becoming  moist,  as  it  would  then  not  separate  quite  as  well.  The 
lead  button  is  then  washed  with  hot  water  or  diluted  sulphuric 
acid,  dried,  and  weighed.  The  slag  is  again  smelted  with  some 
potassium  carbonate  and  flour  or  black  flux  for  about  10  to  12 
minutes,  and  then  poured  out.  The  time  required  for  the  fusion, 
counted  from  placing  the  ore  into  the  pot  to  the  first  pouring 
out,  is  from  10  to  15  minutes.  The  iron  pots  will  bear  from  40 
to  50  operations.  In  many  works  lead  matt  free  from  copper, 
poorer  ores,  and  slag  are  assayed  according  to  this  method. 

England1  (Flintshire) :     500   grains  (32.4   grammes)  of  rich 

i  [Percy,  Metallurgy  of  Lead,  pp.  106-108.— G.] 


£4  ASSAYING. 

galena,  500  grains  sodium  carbonate,  and  50  grains  argol ;  for 
poorer  ores  :  350  grains  of  sodium  carbonate,  150  grains  borax, 
and  50  grains  argol.  The  ore  is  mixed  in  a  mixing  scoop  with 
a  long  spout  (Fig.  7,  p.  30),  with  three-fourths  to  four-fifths  of 
the  quantity  of  the  flux.  The  mixture  is  pushed  to  the  front  of 
the  scoop,  next  to  this  the  remainder  of  the  flux  is  placed,  and 
behind  this  the  borax.  The  whole  is  then  carefully  poured  into 
the  dark  glowing  pot  and  subjected  to  the  fusing  operation  men- 
tioned above.  In  pouring  out  the  contents  the  slag  is  kept  back 
in  the  pot  by  means  of  a  wooden  rod,  and  is  again  fused  with 
20  to  30  grains  of  sodium  carbonate  and  5  to  10  grains  of  argol. 
The  yield  of  lead  from  pure  galena  is  generally  from  84.25  to 
85.25  per  cent.  The  difference  in  the  results  of  the  assay  is 
nearly  the  same  for  the  richest  ores  and  those  yielding  up  to  50 
per  cent.,  but  is  greater  in  poorer  ores.  In  Wales  and  Flintshire 
a  yield  of  75  to  82  per  cent.  Pb  is  obtained  from  pure  galena  by 
placing  10  ounces  troy  of  the  ore  in  a  covered  iron  dish  and  fus- 
ing it  in  an  open  forge  fire. — Bleiberg  in  Carinthia :  50  grammes 
of  ore,  2  tablespoonfuls  of  flux  (3  parts  of  argol,  2  saltpetre, 
1  borax),  a  cover  of  powdered  glass  (or  common  salt),  smelting 
for  12  to  15  minutes,  etc. — Belgium:  10  grammes  of  galena  with 
28  grammes  of  sodium  carbonate  and  5  grammes  borax,  or  10 
grammes  sodium  carbonate  and  10  grammes  argol. — Tarnowitz: 
50  grammes  of  ore,  with  black  flux,  borax,  and  a  covering  of 
salt  resting  upon  a  layer  of  a  little  black  flux.  The  difference 
between  the  separate  assays  is  not  more  than  2  per  cent. — Mech- 
ernich:  25  grammes  of  ore  with  150  grammes  of  borax  and  100 
grammes  sodium  carbonate  and  argol  in  equal  parts.  For  slag 
more  borax,  for  lead  matt  more  soda. 

In  Friedrichshutte,  near  Tarnowitz,  two  lots  of  ore  of  50  grammes 
each  are  melted  down  in  a  wind  furnace  together  with  20  gramm.es 
of  a  flux  consisting  of  8  parts  of  potash,  1  of  flour,  and  10  grammes 
of  borax.  The  buttons  are  accurately  weighed  to  centigrammes,  and 
the  content  of  lead  must  not  vary  more  than  1.5  per  cent.1 

b.  Assay  with  potassium  cyanide  in  clay  crucibles. — This  can 
be  executed  at  comparatively  low  temperatures,  and  gives  a  good 

1  Ztschft.  f.  d.  Bg.,  Httn.  u.  Salinenwesen  im  preuss.  Staate.  Bd.  22,  p.  92. 


ASSAYS   OF   LEAD   IX   THE   DRY   WAY.  85 

yield,  but  is  more  expensive  than  the  foregoing.  Besides,  the 
potassium  cyanide  is  poisonous,  and  adheres  to  the  porous  mass 
of  the  crucible  which  may  uncover  the  lead  button  and  effect  its 
oxidation. 

The  charge,  according  to  Levol,  is  as  follows :  100  parts  galena, 
100  potassium  ferrocyanide,  and  50  potassium  cyanide  with  some 
sodium  carbonate;  according  to  Ricketts:  10  grammes  of  ore,  20 
to  25  grammes  of  potassium  cyanide,  and  a  covering  of  common 
salt.  The  charge  is  fused  for  12  to  15  minutes  at  a  low  tempera- 
ture ;  the  yield  is  78.5  to  79.1  per  cent,  of  lead. 

2.  Galena  with  more  earths. 

a.  Assay  with  black  flux  (potassium  carbonate  and  flour)  and 
metallic  iron,  in  clay  crucibles. — When  the  ore  contains  large 
quantities  of  earth,  more  slag  is  formed.  This,  if  the  contents 
of  the  crucible  were  to  be  poured  out,  would  retain  considerable 
lead,  which  will  settle  if  the  charge  is  allowed  to  cool  off  in  the 
crucible.  The  loss  of  lead  is  from  2  to  3  per  cent.  Deep  cruci- 
bles (Fig.  49,  p.  64)  are  used  for  this  purpose,  and  the  charges 
fused  in  a  muffle  or  wind  furnace.  The  work  can  be  done  more 
conveniently  in  the  latter,  and  fuel  will  also  be  saved.  Should 
small  quantities  of  metallic  sulphides  be  present,  it  is  well  to 
roast  the  ore  somewhat  in  a  covered  crucible  to  volatilize  the 
arsenical  sulphides,  the  sulphur  from  the  iron  pyrites,  etc. 
Charge :  5  grammes  of  galena  are  placed  on  the  bottom  of  the 
crucible,  upon  this  is  put  a  piece  of  iron  wire  4  to  5  millimeters 
thick,  and  up  to  9  millimeters  long  (it  should  be  longer  or  shorter 
according  to  the  percentage  of  lead,  that  is  to  say,  about  25  to  30 
per  cent,  of  the  weight  of  the  ore).  Upon  this  are  placed  15 
grammes  of  black  flux  (or  potassium  carbonate  with  15  to  20 
per  cent,  of  flour)  and,  in  case  of  basic  gangues,  2  to  3  grammes 
of  borax.  Upon  this  comes  a  covering  of  common  salt  5  milli- 
meters thick,  and  on  top  of  all  a  piece  of  charcoal  the  size  of  a 
hazel-nut,  for  maintaining  a  reducing  atmosphere.  The  contents 
of  the  crucible  are  slowly  heated  in  the  muffle  furnace  until  the 
yellow  flame  caused  by  the  carbonization  of  the  flour  is  no  longer 
visible.  The  heat  is  then  raised,  and  tongues  of  bluish  flames 
arising  from  the  carbonic  oxide  will  make  their  appearance.  The 
contents  of  the  crucible  should  not  froth  too  strongly,  and  for 


86  ASSAYING. 

this  reason  the  firing  must  be  done  very  carefully,  especially  when 
low  crucibles  are  used.  When  the  "  flaming"  and  frothing  have 
ceased,  the  heat  is  still  kept  up  for  J  to  f  of  an  hour  to  allow 
the  sulpho-salt  (p.  82)  to  become  decomposed  by  the  metallic 
iron.  25  to  30  minutes  are  required  for  fusing  the  charge.  The 
sample,  fuming  strongly  from  the  vapors  of  the  common  salt,  is 
then  taken  out,  allowed  to  cool  off,  and  freed  from  slag.  By 
hammering  the  lead  flat,  the  iron  adhering  to  it  will  fly  off.  The 
lead  button,  which  is  covered  with  iron  sulphide,  is  then  brushed 
and  weighed.  The  success  of  the  assay  is  indicated  by  the  iron 
still  adhering  to  the  lead  without  this  being  wrapped  around  it 
(to  prevent  this,  the  iron  wire  should  not  be  too  fine),  by 
thoroughly  fused  slag  and  a  malleable  lead  button.  If  brittle, 
it  contains  sulphur.  The  various  assays  must  agree  within  1  to 
3  per  cent,  according  to  the  richness  of  the  ore. 

Freiberg :  3.75  grammes  of  ore,  0.92  to  1.13  grammes  of  iron 
wire ;  7.5  to  9.4  grammes  of  black  flux  or  potassium  carbonate 
with  flour,  1.13  to  1.5  grammes  of  borax,  and  for  basic  gangue 
2.25  to  2.63  grammes  of  glass,  and  a  covering  of  common  salt, 
5  millimeters  thick.  The  charge  is  heated  from  f  to  1  hour  in 
the  wind-furnace. — Pribram:  0.5  gramme  of  crude  argol  is 
placed  in  the  bottom  of  the  crucible,  upon  this  iron  wire,  then  5 
grammes  of  galena,  and  12  grammes  of  black  flux,  and  finally 
a  covering  of  common  salt.  The  charge  is  heated  from  20  to  25 
minutes  in  a  gently  glowing  wind-furnace  until  the  fusing  mass 
subsides.  The  fire  is  then  urged  on,  when  the  assay  will  emit 
gas  (boil)  vigorously,  and,  when  this  is  the  case,  the  firing  is 
continued  for  5  minutes  longer.  A  difference  of  2  per  cent,  is 
allowed  in  the  assay  of  ores  with  0  to  50  per  cent,  of  Pb,  and  3 
per  cent,  in  those  with  over  50  per  cent. — England  :l  The  same 
quantities  of  ore  and  flux  are  used  as  for  assays  in  the  iron  pot 
(p.  82).  The  ore  is  placed  in  a  Hessian  crucible  together  with 
f  to  |  of  the  flux,  and  a  strip  of  wrought  iron  in  the  shape  of  a 
horse-shoe  is  pushed  into  the  mass.  The  crucible  is  gradually 
heated,  requiring  from  20  to  25  minutes,  and  during  this  time 
the  iron  is  moved  about  several  times.  When  the  flux  is  thin 

1  [Percy,  Mettallurgy  of  Lead,  110-112.— G.] 


ASSAYS   OF   LEAD   IN  THE   DRY   WAY.  87 

fluid  the  crucible  is  taken  from  the  furnace,  the  iron,  which 
should  be  free  from  globules  of  lead,  is  removed,  and  the  cru- 
cible allowed  to  cool.  The  contents  are  then  poured  out,  and  the 
lead  button  is  freed  from  slag.  If  the  heat  has  not  been  strong 
enough,  the  lead  button  will  be  hard,  and  will  have  a  lustre  like 
galena,  and  the  slag  will  also  be  covered  with  a  lustrous  film. 
The  yield  of  lead  from  pure  galena  is  from  82  to  83  per  cent,  of 
Pb. — New  York :  10  grammes  of  ore,  25  grammes  of  black  flux, 
three  loops  of  iron  wire,  which  are  taken  out  after  the  fusion  is 
complete,  and  a  covering  of  common  salt.  The  yield  from  pure 
galena  is  78.4  to  78.6  per  cent.,  with  a  difference  of  1  to  2  per 
cent,  in  the  various  assays. —  Upper  Harz :  The  assay  was  form- 
erly conducted  in  the  same  manner  as  in  Freiberg,  but  now  iron 
•pots  are  used. 

b.  Upper  Harz,  assay  with  potassium  carbonate. — A  muffle- 
furnace  is  required  for  this  method  of  assaying.  Low  crucibles 
(Fig.  49)  may  be  used,  as  the  charge  contains  no  carbon,  and 
several  crucibles  can  be  placed  in  the  muffle  at  one  time.  The 
result  of  this  assay  is  not  as  accurate,  the  yield  being  somewhat 
less  than  with  the  methods  described  above,  as  the  success  of  the 
operation  depends  on  the  proper  "cooling  of  the  assay,"  for 
which  there  is  no  guide  but  experience.  This  method  is  there- 
fore chiefly  available  for  uniform  ores  only,  the  approximate 
yield  of  which  is  known.  It  has  been  almost  abandoned  at  the 
present  time. 

Charge:  12.5  to  15  grammes  of  potassium  carbonate  are  placed 
in  a  small  crucible  (Fig.  49,  p.  64).  To  this  are  added  5  grammes 
of  galena,  and  both  are  thoroughly  stirred  together  with  the 
mixing  spatula.  In  case  basic  earths  are  present,  1  assay  spoon- 
ful of  borax  is  placed  upon  the  mixture,  and  upon  this  a  covering 
of  common  salt  5  millimeters  thick.  The  charge  is  then  placed 
in  the  thoroughly  heated  muffle-furnace,  where  it  remains,  with 
the  mouth  of  the  muffle  closed,  until  it  has  come  into  perfect 
fusion  (that  is,  when  no  more  deposits  are  perceptible  on  the 
edges  of  the  crucible).  To  decompose  the  sulpho-salt  by  oxida- 
tion, the  mouth  of  the  muffle  is  then  opened  for  about  10  to  15 
minutes,  until  the  crucible  appears  dark  and  the  vapors  above  it 
have  greatly  diminished  or  entirely  disappeared  (this  is  called 


88  ASSAYING. 

cooling  the  assay).  Thereupon  the  furnace  is  brought  back  to  its 
first  temperature,  completely  closing  the  muffle,  in  order  to  de- 
compose the  still  remaining  sulphurized  lead  by  the  sulphate 
which  has  been  formed.  The  crucible  *  is  then  taken  out  and 
allowed  to  cool  off,  and  the  lead  buttons  are  freed  from  adhering 
slag.  If  the  assay  has  been  successful,  the  slag  is  completely 
fused,  and  the  lead  button  has  a  pure  lead  color,  but  not  much 
metallic  lustre,  as,  if  this  is  the  case,  the  heat  has  been  too 
strong. — For  ore  containing  antimony :  10  grammes  of  ore,  35 
grammes  of  potassium  carbonate,  1  gramme  of  saltpetre,  and  a 
covering  of  common  salt.  30  minutes  are  required  for  fusion,  10 
minutes  for  cooling,  and  10  minutes  for  the  final  heating  of  the 
assay. 

3.  Galena  containing  large  quantities  of  earths. — The  English 
method  (p.  83)  is  employed  with  a  strip  of  sheet-iron  in  the  form 
of  a  horse-shoe,  but  stronger  fluxes  (caustic  alkalies)  are  used, 
which,  to  be  sure,  attack  the  crucibles  more  energetically,  and 
larger  charges,  as  for  instance :  100  grammes  of  assay  sample, 
100  to  150  grammes  of  caustic  soda,  150  to  250  grammes  of  po- 
tassium carbonate  or  sodium  carbonate,  strip  of  iron  in  the  form 
of  a  horse-shoe,  25  millimeters  wide,  and  4  millimeters  thick. 
From  1  to  1 J  hours  are  required  for  perfect  fusion,  and  until  the 
iron  is  free  from  lead  globules. 

J9.  Lead  monosulphide  with  foreign  metallic  sulphides  (galena 
with  zinc  blende,  pyrites,  etc. ;  lead  matt,  etc.). 

1.  Roasting  and  reducing  assay. — The  result  of  this  assay  is 
inaccurate,  as  the  lead  oxide  is  liable  to  slag  off  and  foreign  me- 
tallic oxides  to  be  reduced,  the  metal  of  which  contaminates  the 
lead.  For  this  reason  the  assay  with  sulphuric  acid  is  frequently 
used  instead  (Rammelsberg  smelting  works  in  the  Lower  Harz). 

In  the  Lower  Hungarian  works  and  in  the  Klausenburg  district 
this  assay  is  used  as  a  checking  assay.  (Einlosungsprobe.)  No 
iron  is  added,  but  the  ore  is  roasted  as  completely  as  possible  with 
the  addition  of  coal  dust.  In  Schemnttz  the  following  differences 
are  allowed : — 

Amount  of  lead  in  the  ore.  Difference  allowed. 

Up  to  30  per  cent. 2  per  cent. 

Up  to  40  .         .         .         .         .     4 
Over  40         "  6        " 


ASSAYS   OF   LEAD   IN   THE   DRY   WAY.  89 

The  assays  are  repeated  three  times. 

The  allowances  used  in  the  Klausenburg  mining  district1  differ 
but  little  from  the  above. 

Amount  in  the  ores.  Differences  allowed. 

0  to  25  per  cent 2  per  cent. 

25.25  to  50       "  4       " 

50.25  per  cent,  to  the  maximum  content        .6       " 

Five  grammes  of  ore  are  roasted  in  a  roasting  dish.  This  is 
mixed  in  the  assay  vessel  with  7.5  to  15  grammes  of  potassium 
carbonate  and  flour,  or  black  flux.  Upon  this  is  placed  1.25  to 
1.5  grammes  of  glass,  then  0.25  to  0.5  grammes  of  thick  iron 
wire,  upon  this  1.25  to  1.5  grammes  of  borax,  then  a  covering  of 
common  salt,  and  on  top  of  all  a  piece  of  coal.  By  fusing  the 
roasted  charge  in  the  muffle-  or  wind-furnace  at  not  too  high  a 
temperature,  the  lead  oxide  and  lead  sulphate  are  reduced  (if  the 
temperature  is  too  high,  many  other  metallic  oxides  are  also  re- 
duced), and  the  foreign  oxides  and  earths  contained  in  the  sample 
are  slagged  off  by  the  aid  of  the  potassium  carbonate  in  the  black 
flux,  as  well  as  of  the  borax  and  glass.  The  heating  should  be 
done  with  the  greatest  care,  as  the  contents  swell  up  very  much. 
20  to  30  minutes  are  required  for  smelting  in  the  muffle-furnace 
after  the  "flaming"  in  the  muffle  has  ceased,  and  from  15  to  20 
minutes  in  the  wind-furnace  after  the  flames  get  under  way. 

Hungary:  10  grammes  of  roasted  ore  are  charged  with  11.5 
grammes  of  black  flux,  and  this  is  covered  with  a  layer  of  15  to 
20  grammes  of  common  salt.  It  is  fused  by  keeping  up  a  strong 
fire  under  the  muffle  for  half  an  hour.  The  yield  is  from  10  to 
12  per  cent.  Pb  less  than  from  an  assay  with  metallic  iron.  It 
will  be  larger  if  charcoal  dust  is  added  in  roasting,  but  the  but- 
ton will  be  less  pure. 

2.  Assay  with  sulphuric  add  (combined  dry  and  wet  method). — 
This  gives  more  accurate  results  than  the  foregoing  processes,  as 
the  foreign  metals  are  removed  before  fusion,  but  there  will  be 
always  a  loss  of  lead  in  the  last-named  operation. 

Five  to  10  grammes  of  the  ore  are  ground  as  fine  as  possible.  It 
is  decomposed  by  digesting  it  with  mtro-muriatic  acid  (aqua 
regia)  in  a  glass  flask  with  straight  walls  (Fig.  16,  p.  39).  A 

1  Fortschritte  iin  Probirwesen.     Balling.     Berlin,  1887,  p.  118. 


90  ASSAYING. 

few  drops  of  sulphuric  acid  are  added,  and  it  is  then  evaporated 
to  dryness.  The  dry  mass  is  digested  with  diluted  sulphuric  acid, 
filtered,  and  washed.  The  filter  is  freed  from  water  between 
blotting-paper,  and,  with  the  residuum  (lead  sulphate  and  insolu- 
ble earths,  clay,  etc.),  is  dried  in  a  roasting  dish  under  the  muffle, 
and  finally  incinerated  at  as  low  a  temperature  as  possible.  The 
mass  is  then  ground  'up,  and  charged  in  a  high  crucible  with  15 
grammes  of  black  flux  (1  part  saltpetre  and  3  parts  argol),  and 
then  with  1  to  1.5  grammes  of  iron.  The  charge  is  slowly  heated, 
and  then  strongly  heated  after  the  "  flaming"  in  the  muffle  has 
ceased  (15  to  20  minutes). — If  the  assay  sample  should  contain 
antimony,  which  partly  remains  as  lead  antimoniate  with  the  lead 
sulphate,  the  process  is  as  follows :  The  assay  sample  is  decom- 
posed by  nitric  acid,  to  which  some  tartaric  acid  has  been  added. 
It  is  neutralized  with  sodium  carbonate,  and  the  antimony  is  ex- 
tracted by  digesting  the  mass  for  about  half  an  hour  in  a  solution 
of  sodium  sulphide  containing  sulphur.  It  is  then  filtered  and 
washed,  and  the  residuum  is  treated  in  the  same  manner  as  in  the 
sulphuric  acid  assay. 

II.   Oxidized  Substances. 

A.  Lead  oxides  free  from  earths  (litharge,  minium,  skimmings 
(Abstrich),  etc.). — 5  grammes  of  the  sample  are  fused  at  not  too 
high  a  temperature  with  12.5  to  15  grammes  of  potassium  car- 
bonate with  30  to  35  per  cent,  of  flour,  or  black  flux,  and  cover- 
ing of  common  salt,  with  small  pieces  of  coal  on  the  top,'  in  the 
same  manner  as  in  the  roasting  and  reducing  assay.  If  the 
sample  should  contain  any  sulphur,  0.25  to  0.5  gramme  of  iron 
wire  is  added.  20  to  25  minutes  are  required  for  fusion  in  the 
muffle-furnace  after  the  "flaming"  in  the  muffle,  and  13  to  15 
minutes  in  the  wind-furnace  after  the  flame  is  under  way. 

-B.  Lead  oxides  with  earths. — The  charge  is  the  same  as  in  II. 
A,  with  the  exception  that  from  25  to  30  per  cent,  of  borax  is 
added,  and  from  5  to  10  minutes  more  is  required  for  fusion. 

C.  Salts  of  lead  oxide,  namely  : — 

1.  Lead  carbonate  (cerussite),  lead  chr ornate  (crocoisite),  lead 
phosphate  (pyromorphite),  mimetene  (lead  ar senate),  and  yellow 


ASSAYS   OF   LEAD   IN   THE   DRY   WAY.  91 

fend  ore  (widfentie). — The  charge  is  the  same  as  in  II.  A,  with  :ni 
addition  of  from  20  to  30  per  cent,  of  borax,  according  to  the 
presence  of  more  or  less  earthy  substances.  With  pyromorphite 
containing  arsenic  from  5  to  10  per  cent,  of  iron  is  added  to  sepa- 
rate the  arsenide  of  iron.  Time  for  fusion  the  same  as  in  II.  A. 
Charges  for  oxidized  ores  according  to  Percy:  500  grains  of 
ore,  350  grains  of  sodium  carbonate,  150  grains,  or  less,  of  borax, 
and  50  grains  of  argol.  The  charge  is  fused  in  an  iron  pot 
(p.  82). — Lead  carbonate  (cerussite) :  500  grains  of  ore,  500  grains 
of  sodium  carbonate,  100  grains  of  argol,  and  30  grains  of  borax. 
The  charge  is  fused  for  about  20  minutes  in  a  clay  crucible  in  the 
wind-furnace,  and  poured  out  (p.  86). — Lead  phosphate  (pyro- 
morphite) :  300  grains  of  ore,  400  grains  of  sodium  carbonate,  20 
grains  of  powdered  charcoal,  and  30  grains  of  borax ;  or,  350 
grains  of  sodium  carbonate,  100  grains  of  argol,  30  grains  of 
borax,  and  some  metallic  iron.  Fusing  time :  25  to  30  minutes, 
counting  from  introducing  the  charge  until  it  is  poured  out.1 

2.  Lead  sulphate  (anglesite,  lead  fume,  dross,  sweepings,  tailings, 
skimmings,  etc.}. — The  charge  is  the  same  as  for  the  assay  with  sul- 
phuric acid  (p.  89).     If  necessary,  a  smaller  quantity  of  metallic 
iron  (for  instance,  only  10  per  cent,  for  fume  and  skimmings, 
which  carry  but  little  sulphate)  is  used,  and  20  to  30  per  cent,  of 
borax  is  added  if  earths  are  present. 

3.  Lead  silicate  (slags). — 10  grammes  of  slag  are  ground  as 
fine  as  possible,  and  mixed  in  an  assay  vessel  with  15  grammes  of 
potassium  carbonate  with  30  to  35  per  cent,  of  flour.    Upon  this, 
in  case  of  acid  slags  are  placed  1  to  2  grammes  of  borax.     For 
basic  slags,  2.5  to  5  grammes  of  borax,  or  equal  parts  of  glass 
and  borax,  are  taken,  and  for  slag  containing  sulphur,  and  which 
may  not  have  been  previously  roasted,  0.25  to  0.5  gramme  of  iron 
and  a  covering  of  salt  with  a  piece  of  coal.     The  charge  is  melted 
in  a  tall  crucible  (Fig.  49,  p.  64),  such  as  is  used  in  the  roasting 
or  reducing  assays,  or  in  the  crucible  shown  in  Fig.  52,  p.  67. 
1  to  1 J  hours  are  required  for  smelting  acid  slags  in  muffle-fur- 
nace, and  f  to  1  hour  for  basic  slags  in  the  wind-furnace  after  the 
flame  is  free.     A  thin   liquid  fusion  is  absolutely  necessary,  so 

i  Percy,  Metallurgy  of  Lead,  pp.  112,  113. 


92  ASSAYING. 

that  the  lead  globules  can  unite,  this   being  the   reason  why  a 
longer  smelting  is  required. 

III.  Alloys  of  Lead. 
The  wet  method  must  be  employed  for  assaying  alloys  of  lead.1 

26.    WET   ASSAYS. 

These,  if  accurate  results  are  .to  be  obtained,  are  tedious,  re- 
quire much  time,  and,  as  a  necessary  condition,  require  the  ab- 
sence of  certain  substances.  These  processes  resemble  the 
manipulations  occurring  in  chemical  analysis,  and  for  this  reason 
we  shall  give  here  only  processes  which  can  be  easily  carried  out. 

A.  Assay  by  gravimetric  analysis. 

1.  Assays  in  Bleiberg  in  Carinihia  and  other  places.2 — 2 
grammes  of  galena  are  powdered  as  fine  as  possible,  and  heated 
with  nitric  acid.  When  red  vapors  cease  to  come  off,  the  mass  is 
evaporated  nearly  to  dryness  with  a  few  drops  of  sulphuric  acid. 
If  much  lime  is  present,  it  is  diluted  with  J  of  a  liter  of  water  be- 
fore the  sulphuric  acid  is  added,  and  the  evaporation  with  the  nitric 
acid  is  not  carried  too  far  in  order  to  keep  as  much  as  possible  of 
the  lime  in  solution.  It  is  then  allowed  to  cool  off,  diluted,  fil- 
tered, and  washed  until  the  acid  reaction  of  the  wash-water 
ceases.  The  contents  of  the  filter  (lead  sulphate  and  insoluble 
earths,  sulphur,  etc.)  are  then  rinsed  off  into  a  beaker  glass,  and 
digested  with  a  concentrated  solution  of  neutral  sodium  carbo- 
nate to  convert  the  lead  sulphate  into  carbonate.  It  is  then  fil- 
tered and  washed  until  the  water  does  not  become  clouded  by  the 
addition  of  barium  chloride.  The  residuum  is  heated  with  di- 
luted nitric  or  acetic  acid  to  extract  the  lead,  filtered,  and  the 
filter  is  washed  with  hot  water  until  acid  reaction  ceases.  The 
lead  is  then  precipitated  from  the  filtrate  with  as  small  a  quantity 
of  sulphuric  acid  as  possible,  to  prevent  a  precipitation  of  lime 

1  Analysirmethoden    fur   Blei ;  Fresenius's  Ztsclir.  viii.   118   (Fresenius)  ; 
Preuss.  Ztschr.  x.  125  (Hampe). 

2  B.  u.  h.  Ztg.  1871,  p.  62. 


LEAD — WET   ASSAYS.  93 

with  it.  The  lead  sulphate  is  filtered,  washed  with  hot  water,  and 
dried.  It  is  then  detached  from  the  filter,  heated  to  a  red  heat 
and  weighed.  There  should  be  at  the  utmost  a  difference  of  0.1 
per  cent,  between  assays  and  counter-assays.  Another  process  is 
as  follows :  The  ore  is  dissolved  in  nitre-muriatic  acid  (aqua 
regia)  and  evaporated  to  dryuess.  The  lead  chloride  (as  also  the 
ferric  chloride  and  copper  chloride)  is  extracted  by  boiling  water 
and  filtered.  The  filtrate  is  neutralized  with  ammonia  to  a  pre- 
cipitating point.  The  lead  is  precipitated  with  dilute  sulphuric 
acid,  and  alloAved  to  stand  quietly  for  6  hours.  The  lead  sulphate 
is  then  filtered  and  washed,  the  filter  dried  and  burned,  and  the 
sulphate  heated  and  weighed. 

2.  Mohr's process. — 1  gramme  of  finely  powdered  galena  is  boiled 
in  a  glass  or  porcelain  vessel  with  hydrochloric  acid.  To  this  is 
added  a  small  piece  of  zinc,  and  the  contents  of  the  vessel  are  then 
heated  until  the  fluid  becomes  clear.  The  precipitated  lead  is 
washed  by  decantation  and  dissolved  in  diluted  nitric  acid.  It  is 
then  filtered  to  free  it  from  adhering  insoluble  substances  (quartz, 
heavy  spar,  etc.).  The  filtrate  is  very  much  diluted  with  water, 
and  the  lead  is  precipitated  as  lead  sulphate  with  sulphuric  acid 
in  the  same  manner  as  in  1. 

Storer1  weighs  the  lead  precipitated  with  zinc,  directly  or  dis- 
solves it,  in  case  it  contains  insoluble  admixtures,  in  nitric  acid, 
then  weighs  the  residue  and  obtains  the  weight  of  the  lead  from 
the  difference.  Mascazzini2  fuses  the  impure  lead,  which  has  been 
dried,  with  a  mixture  1J  to  2  parts  of  caustic  alkali,  5  parts  of 
borax,  and  5  parts  of  starch.  Lowe3  frees  the  lead  sulphate  from 
its  admixtures  with  earths  by  dissolving  it  in  sodium  hyposulphite, 
precipitates  it  as  sulphide  with  sulphuretted  hydrogen,  and  con- 
verts this  into  sulphate.  Biche4  determines  the  lead  as  superoxide 
by  electrolysis.  The  galena  is  dissolved  in  hydrochloric  acid. 
The  clear  solution  is  filtered  into  diluted  sulphuric  acid,  and  the 
lead  determined  as  sulphate.  But  this  must  be  ignited  gently  to 

1  Storer,  in  Fresenius's  Ztschr.,  ix.  514;  B.  u.  h.  Ztg.  1870,  p.  208;  1873, 
p.  91. 

2  Mascazzini,  in  Dingier,  ccvii.  46  ;  B.  u.  h.  Ztg.  1878,  p.  382. 

3  B.  u.  H.  Ztg.  1874,  p.  322. 

4  B.  u.  h.  Ztg.  1878,  382. 


94  ASSAYING. 

prevent  the  volatilization  of  traces  of  lead  chloride  which  may  be 
present,  as  this  would  make  the  result  less  accurate. 

B.  Volumetric  processes.1 — These  have  been  frequently  proposed 
without  any  practical  success. 

C.  Colorimetric  processes. — Bischof2  has  given  a  method  for 
determining  small  quantities  of  lead,  which  is  based  upon  the 
browning  of  a   solution   containing   lead,  by  sulphuretted   hy- 
drogen. 

D.  Electrolytic  processes. — Parodi  and  Mascazzini  proceed  as 
follows  :3  The  lead  is  first  separated  as  sulphate  and  then  dissolved 
by  an  alkaline  solution  of  sodium  tartrate.     A  measured  portion  of 
this  solution  is  acidulated  with  hydrochloric  acid  until  a  white  pre- 
cipitate forms,  then  neutralized  with  sodium  carbonate,  and  after 
30  c.c.  (150  grammes  in  ^  liter)  has  been  added,  the  whole  is  diluted 
with  ammonia  to  200  c.c.     The  platinum  electrodes  are  then  placed 
in  the  solution  and  the  galvanic  current  allowed  to  act.     Precipita- 
tion being  finished,  after  washing  the  cone  thoroughly  without  in- 
terrupting the  current,  the  current  is  stopped,  and  the  precipitate 
upon  the  cone  is  twice  washed  with  water  and  alcohol,  and  dried  at 
a  temperature  of  from  30°  to  40°  C.  in  an  atmosphere  of  illumina- 
ting gas.     The  lead  precipitated   by  electrolysis  dissolving  with 
some  difficulty  in  nitric  acid,  it  is  recommended  to  repeat,  if  neces- 
sary, the  dissolving,  and  also  to  weigh  the  platinum  cone  before  and 
after  the  solution  of  the  lead,  in  order  to  be  sure  that  no  more  ad- 
heres to  it. 

According  to  Kiliani,4  the  precipitate  of  superoxide  of  lead  ad- 
heres tightly  to  the  anode  in  large  quantities  only  when  the  strength 
of  the  current  is  so  slight  that  no  evolution  of  gas  takes  place  along 
with  the  separation.  If  there  is  an  evolution  of  gas,  the  precipitate 
exfoliates  in  scales  from  the  anode.  With  such  a  weak  current  the 
precipitation  is  slow ;  it  is  therefore  advisable  to  use  a  dish  as  an 
anode  (see  Fig.  68)  and  a  cone  or  disk  as  a  cathode.  This  arrange- 
ment enables  the  precipitate  to  be  washed  with  ease  and  without 
loss.  The  precipitate  is  not  a  pure  superoxide,  but  a  hydrate  with 

1  Mohr,  Lehrbuch  der  Titrirmethode,  1874  p.  460  ;  Fleischer,  Titrirmethode, 
1876,  pp.  42,  87,  293  ;  Mitchell,  Practical  Assaying,  1868,  p   397. 

2  Fresenius's  Ztschr.  1879,  p.  43;  B.  u.  h.  Ztg.  1879,  p.  187. 

3  Gazetta  chim.  ital.  8.     Ztschft.  f.  anal.  Chem.  Bd.  18  p.  588. 

4  Bg.  u.  Httnmsch,  Ztg.  1883,  p.  401. 


COPPER ORES.  95 

a  varying  content  of  lead,  which,  according  to  Wernicke,1  contains 
the  more  anhydrous  hyperoxide  the  more  concentrated  the  liquid 
and  the  longer  the  electrolytic  action  has  lasted.  By  heating  this 
precipitate  at  200°  to  250°  C.,  until  the  weight  is  constant,  there 
remains,  according  to  Kiliani,  pure  superoxide,  no  decomposition 
taking  place.  In  drying  and  cooling  the  dish  should  be  covered, 
otherwise  small  particles  of  the  oxide  might  be  thrown  out. 

According  to  Schucht,2  the  complete  separation  of  all  the  lead  as 
superoxide  takes  place  only  in  the  presence  of  at  least  10  per  cent, 
free  HN03. 

Tenney3  confirms  this  observation.  In  the  presence-  of  large 
quantities  of  lead  a  platinum  dish  should  always  be  used  as  a  posi- 
tive electrode.  Too  much  HN03,  however,  is  injurious,  as  by  its 
decomposition  the  nitrous  acid  formed  can  redissolve  only  a  portion 
of  the  lead  oxide. 

May  recommends  to  rub  off  the  precipitated  superoxide  from  the 
positive  electrode,  with  a  bit  of  rubber  tube  on  a  glass  rod,  into  a 
beaker  containing  a  little  water.  The  filtered  precipitate,  after  the 
filter  has  been  burnt  separately,  is  ignited  to  PbO  in  a  porcelain 
crucible.  If  a  portion  of  the  superoxide  adheres  firmly  to  the  posi- 
tive electrode,  this  is  also  converted  into  PbO  by  careful  heating  of 
the  electrode.  The  determination  as  superoxide  is,  however,  pre- 
ferable. It  should  be  remembered  that  the  superoxide  must  be 
washed  without  interrupting  the  current  to  avoid  loss.4 

II,  Copper, 

27.    ORES. 

Native  copper. — Sulphuretted  ores  :  copper  glance,  Cu2S,  with 
97.7  Cu ;  erubescite  (purple  copper  ore}\  Cu3FeS3,  with  55.6  Cu ; 
copper  pyrites,  CuFeS2,  with  34.6  Cu.  Ores  with  antimony  or 
arsenic  :  tetrahedrite  (J^a/fez),  R4Q2S7  (in  which  R  =  Cu2,  Ag2Fe, 
Zn,  Hg,  etc.,  Q  =  Sb,  As),  with  15  to  48  Cu,  as  much  as  30  per 
cent,  silver,  and  from  0  to  18  per  cent,  mercury;  bournonite, 

1  Poggendorff,  Anal.  Bd.  141,  p.  109. 

2  Ztschft.  f.  anal.  Chem.  Bd.  22,  p.  487. 

3  Am.  Chem.  Journ.  vol.  5,  p.  415. 

4  Classen,  Chem.  Analysis  by  Electrolysis.     Trans.  1887,  p.  69. 


OF  THE     "^ 

UNIVERSITY 

OF 


Ub  ASSAYING. 

PbCuSbS3,  with  13.03  Cu  and  42.54  Pb;  enargite,  Cu3AsS4, 
with  48.6  Cu.  Oxidized  copper  ores  :  cuprite  (red  copper),  Cu2O, 
with  88.8  Cu;  malachite,  CuCO4  +  H2O,  with  58  Cu;  azurite, 
Cu3C2O7  +  H2O,  with  35.7Cu  ;  dioptase  (Kieselmalachit),  CuSiO3+ 
2H2O,  with  35.7  Cu ;  atacamite  Cu4O3Cl2  +  3H2O,  with  59.4  Cu  ; 
phosphates  of  copper,  with  30  to  56  Cu ;  ar senates  of  copper,  with 
25  to  50  Cu ;  cupric  sulphate  or  blue  vitriol,  CuSO4  +  5H2O,  with 
25.3  Cu. 

28.    DRY  ASSAYS.1 

These,  besides  consuming  much  time,  and  being  expensive,  re- 
quire great  experience  and  are  less  accurate  than  the  wet  assays, 
which  are  now  much  employed  in  smelting  works  for  valuing 
ores.  There  are  two  methods,  known  as  the  German  and  the 
Cornish  assay.  Both  are  based  upon  the  principle  that  copper 
has  a  stronger  affinity  for  sulphur,  and  less  for  oxygen,  than  the 
foreign  metals  (iron,  zinc,  antimony,  lead,  arsenic,  etc.)  with 
which  the  ores  are  contaminated,  so  that,  when  they  are  present 
in  an  oxidized  condition,  or  have  been  converted  into  it  by  roast- 
ing, they  are  mostly  slagged  off  at  comparatively  low  temperatures 
on  being  fused  (reducing  fusion)  with  reducing  agents  (black  flux 
free  from  sulphur,  potassium  carbonate  and  flour)  and  solvent 
agents  (borax,  glass),  and  only  a  very  small  part  of  them  passes  into 
the  reduced  copper  (black  copper).  The  latter  during  the  subse- 
quent oxidizing  fusion  (refining)  eliminates  the  foreign  metals  in 
an  oxidized  condition,  and  is  itself  transformed  into  refined  copper, 
while  the  metallic  oxides  which  have  been  formed  are  either 
slagged  off  by  the  solvent  agent  (borax)  or  are  carried  into  the 
cupel  by  the  lead  oxide.  On  account  of  the  high  temperature  at 
which  copper  fuses,  it  is  well  to  add  in  the  reducing  fusion  collect- 
ing and  liquefying  agents  (such  as  antimony  and  arsenic,  but  lead 
is  less  well  adapted  as  it  may  cause  losses  in  the  refining).  The 
German  and  Cornish  or  English  methods,  which  undergo  modi- 
fications according  as  the  copper  is  combined  with  sulphur, 

1  [Percy.    Metallurgy  of  Copper,  Zinc,  and  Brass.    London,  1861.    pp.  454- 
478.— G.] 


COPPER — DRY   ASSAYS.  97 

antimony,  or  arsenic,  or  is  oxidized  or  alloyed,  are  still  practised 
in  smelting  works,  and  give  results  which  suffice  for  the  business 
of  working  copper  on  a  large  scale. 

A.   German  copper  assay. 

1.   Ores  with  sulphur,  antimony,  or  arsenic. 

a.  Roasting. — Dead  roasting  5  grammes  of  ore,  or  enough  of  it 
is  dead  roasted  that  the  refined  button  of  copper,  to  be  turned  out 
on  the  refining  dish,  does  not  weigh  much  over  0.5  gramme.     It 
is  then  repeatedly  rubbed  up  and  treated  with  coal  and  finally 
with  ammonium  carbonate  for  completely  removing  the  sulphur 
(p.  33)  which  otherwise   would   produce  copper  sulphide   and 
occasion  losses  during  reducing  fusion.     A  well-roasted  sample 
should  be  earthy  (without  metallic  lustre),  have  a  brownish  or 
black  color,  should  not  appear  sintered,  and  should  neither  fume 
nor  smell. 

Pyrites  is  rubbed  up  two  or  three  times  and  treated  once  with 
powered  charcoal — Tetrahedrite,  Fahlerz  (Hungary),  10  grammes 
of  ore  are  rubbed  up  ten  to  twelve  times  at  a  very  low  roasting 
temperature,  taking  them  out  whenever  they  commence  to  fume. 
The  ore  is  then  roasted  without  charcoal  for  f  to  1  hour  at  a 
temperature  not  above  red  heat,  rubbed  up,  and  roasted  for  1 
hour  more  at  a  white  heat. 

b.  Reducing  and  solvent  fusion. — The  roasted  ore  is  well  mixed 
in  an  iron  mortar  with  J  of  the  required  quantity  of  black  flux 
(consisting  of  2  to  2  J  parts  of  argol  and  1  part  of  saltpetre,  or  of 
3  parts  of  potassium  carbonate  and  1  part  of  flour),  a  collecting 
agent  (antimony  is  the  best),  and,  if  the  ore  contains  no  iron,  some 
iron  filings  are  added  to  decrease  the  slagging  of  copper  in  re- 
fining it  on  the  dish.     The  mixture  is  poured  by  means  of  the 
mixing  scoop  (Fig.  6,  p.  30)  into  a  suitable  crucible  of  refractory 
clay  (Fig.  52,  p.  65).    The  remaining  §  of  the  flux  is  then  added, 
upon  this  is  placed  a  mixture  of  borax  and  glass,  then  a  covering 
of  common  salt  and  a  small  piece  of  charcoal. 


98 


ASSAYING. 


Examples  of  Charges. 


Black 
flux. 

Borax. 

Glass. 

Antimony 
(arsenic). 

Iron 
filings. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Pyrites  (copper)  .... 
Purple  copper  ore  .... 
Tetrahedrite  ...  . 

300 
300 
300 

50 
40 
30 

40 
40 
25 

10 
10 
6 

8 

Matt  rich  in  iron  .... 

300 

40  to  50 

40 

10 

Matt  rich  in  copper  .  .  . 

300 

— 

50  to  100 

5 

Charges  suitable  in  many  cases  :  5  grammes  of  ore,  12.5  to  15 
grammes  of  black  flux,  0.3  gramme  of  antimony,  1.25  grammes 
(1  small  assay  spoonful)  of  borax,  1.5  to  2.5  grammes  of  glass, 
and  10  to  15  grammes  of  common  salt;  or  5  grammes  of  roasted 
ore  are  mixed  with  the  same  quantity  of  black  flux  and  put  into 
the  crucible.  Upon  this  are  placed  8  to  10  grammes  of  black  flux, 
1  gramme  of  borax,  2.5  grammes  of  glass,  and  a  covering  of 
common  salt  six  millimeters  thick.  Hungarian  fahlerz :  Half  of 
the  roasted  sample — 5  grammes  are  mixed  with  7  to  8  grammes  of 
black  flux.  The  mixture  is  placed  upon  the  same  quantity  of 
black  flux  in  the  crucible  and  covered  with  common  salt. 

American  charge:  10  grammes  of  ore  are  roasted  and  mixed 
with  20  grammes  of  black  flux,  3  grammes  of  borax  glass,  and 
10  to  20  grammes  of  hematite.  Upon  this  are  placed  10  grammes 
of  black  flux,  3  grammes  of  wood  charcoal,  and  a  covering  of 
common  salt.  Charge  for  unroasted  ores  containing  heavy  spar 
and  gypsum :  5  grammes  of  ore,  5  grammes  of  borax  glass,  5 
grammes  of  powdered  glass,  and  ten  per  cent,  of  rosin ;  and,  be- 
sides for  poor  ores,  25  per  cent,  of  iron  pyrites,  if  this  is  not 
already  present  in  the  ore.  The  whole  is  covered  with  common 
salt  and  fused  to  matt,  which  is  then  roasted  and  treated  as 
above. 

Time  required  for  fusion :  f  to  1  hour  in  a  red  heat  in  the 
muffle-furnace  after  the  "  flaming"  has  ceased,  or  in  a  wind-fur- 
nace after  the  flames  are  free.  The  charcoal  should  be  piled  high 
in  front  of  the  crucibles  in  the  muffle.  Indications  of  a  successful 
assay  are :  a  well-fused  regulns  (which  on  account  of  its  brittle- 


COPPER — DRY  ASSAYS.  99 

ness  must  be  carefully  freed  from  slag),1  without  a  black  coating 
of  brittle  matt  rich  in  copper,  well-fused  slag,  whose  color  may  be 
black  or  green,  but  must  not  be  red,  and  without  an  admixture  of 
metallic  grains. 

c.  Refining. — This  consists  in  an  oxidizing  fusion,  during 
which  the  foreign  metallic  oxides  are  sooner  oxidized  than  the 
copper,  and  are  easily  separated,  either  at  once  as  easily  fusible 
masses,  though  this  is  seldom  the  case,  or  must  be  dissolved  by 
fluxes  (borax,*  lead  oxide),  and  then  separate  with  these  as  slag 
(refining  with  borax  on  the  refining-dish),  or  are  absorbed  by  the 
cupel  (refining  with  lead). 

Lead  is  pre-eminently  oxidizable.  The  lead  oxide  yields  its 
oxygen  to  the  foreign  metals.  It  therefore  acts  as  a  vigorous 
oxidizing  agent,  and  produces  easily  fusible  combinations,  but  it 
contributes  to  the  slagging  off  of  the  copper,  and  for  this  reason 
the  refining  process  with  lead  is  less  accurate  than  that  with  borax 
without  lead,  ferrous  oxide,  antimony,  and  arsenic  protect  cop- 
per from  slagging.  Nickel  and  cobalt  are  difficult  to  separate 
from  copper,  and  do  so  only  at  the  expense  of  considerable  cop- 
per, which  is  slagged  off  (see  assay  of  Nickel).  Tin  and  zinc  give 
refractory  oxides  and  slags,  and,  if  present  in  large  quantities,  the 
wet  method  must  be  employed.  Gold  and  silver  remain  in  the 
refined  copper. 

a.  Refining  on  the  dish.  a.  With  borax. — This  is  the  most  accu- 
rate process  (to  within  1  to  J  per  cent.),  and  is  principally 
adopted  for  black  copper  free  from  lead,  or  which  contains  iron, 
arsenic,  or  antimony.  According  to  the  size  and  impurity  of  the 
copper  button,  1.25  to  2.5  grammes  of  borax  glass  are  placed, 
either  wrapped  up  in  a  cornet,  or  by  means  of  an  iron  spoon,  in 
a  refining-dish,  which  stands  in  the  white-hot  muffle,  and  is  sur- 
rounded by  glowing  coals.  The  copper  button,  weighing  from 
0.5  to  0.6  gramme,  is  taken  up  with  the  curved  tongs  (Fig.  49, 
p.  64)  and  placed  in  the  dish.  The  mouth  of  the  muffle  is  then 
closed  by  a  plug,  or  by  piling  coal  in  front  of  it,  and  the  button 
is  fused  quickly  at  as  high  a  temperature  as  possible.  The  mouth 

1  [As  soon  as  the  slag  has  solidified,  or  has  "set,"  the  crucible  is  plunged 
into  cold  water  several  times,  and  then  left  to  cool.  This  immersion  in  water 
cracks  the  slag,  and  causes  the  regulus  to  he  more  easily  removed. — G.] 


1 00  ASSAYING. 

of  the  muffle  is  then  slightly  opened  to  allow  of  the  access  of  air. 
On  account  of  the  oxidation  of  the  foreign  metals  (iron,  zinc,  etc.), 
the  button  will  at  first  appear  dull,  but  brightens  as  soon  as  the 
foreign  metals  (with  the  exception  of  antimony  and  arsenic)  have 
been  removed,  and  fumes  from  the  antimony  or  arsenic,  which 
may  have  been  originally  present,  or  has  been  added  as  a  collect- 
ing agent.  (The  first  fumes  more  strongly  than  the  latter,  there- 
fore indicating  the  end  of  the  process  more  plainly.)  The 
completion  of  the  refining  process  may  be  recognized  by  the  but- 
ton, which  remains  bright,  ceasing  to  fume  (should  the  process  be 
continued  the  button  would  become  dull  from  a  covering  of  cu- 
prous oxide) ;  and  also,  by  the  subsiding  of  the  slag,  that  is,  if 
the  button  is  not  too  large,  and  does  not  weigh  much  over  0.4  to 
0.5  gramme.  The  dish  is  then  taken  out  with  the  curved  tongs 
(Fig.  59,  p.  72),  and  carefully  cooled  off  upon  water  until  it  ceases 
to  glow,  and  then  in  water,  and  the  button  freed  from  slag.  The 
assay  is  considered  successful  if  the  button,  on  being  flattened, 
shows  itself  ductile  to  a  certain  extent,  and  has  a  flesh-red  color 
exteriorly.  (A  small  residue  of  antimony  and  arsenic  prevents 
the  button  from  being  entirely  ductile,  and  it  causes  its  fracture 
to  be  gray,  and  equalizes  small  losses  in  slagging  off.)  The  slag 
should  not  be  red,  or  at  least  scarcely  perceptibly  so,  except  at 
the  place  where  the  button  has  lain.  Red  slag  indicates,  either 
that  the  oxidizing  process  has  been  carried  too  far,  or  an  absence 
of  iron  which  otherwise  protects  the  copper  from  slagging  off  dur- 
ing the  reducing  fusion,  as  well  as  during  refining. 

b.  By  itself,  without  borax  and  lead  (Hungarian  speiss  assays)1 
for  buttons  containing  more  antimony  or  lead. — The  copper  but- 
ton is  placed  on  the  white-hot  refining-dish  (p.  64)  standing  in 
the  muffle,  and  is  fused  quickly  at  as  high  a  temperature  as 
possible  after  the  mouth  of  the  muffle  has  been  closed.  After  the 
fusion  is  complete  the  mouth  of  the  muffle  is  opened,  the  register 
is  closed,  and  the  dish  turned  and  lifted.  This  will  cause  the 
slag  formed  from  foreign  oxides  to  remain  behind,  and  the  button 
to  roll  upon  a  place  free  from  slag.  The  refining  is  continued  in 
this  manner  until  the  fuming  ceases,  and  the  now  refined  button 

i  B.  u.  h.  Ztg.  1866,  No.  28 ;  1868,  No.  12;  1871,  p.  255. 


COPPER — DRY  ASSAYS.  101 

assumes  a  sea-green  color.  The  refining-dish  is  then  pulled 
slowly  towards  the  mouth  of  the  muffle,  and  taken  out  as  soon 
as  the  button  brightens.  The  dish  is  then  dipped  in  hot  water, 
when  the  button  can  be  hammered  out  without  cracking  on  the 
edges.  It  should  have  a  red  color.  It  is  now  weighed,  and  the 
difference  in  weight  between  it  and  the  black  copper  determined. 
From  this  the  loss  of  copper,  which  must  be  placed  to  the  account 
of  the  copper,  is  calculated  by  allowing  for  plumbiferous  copper 
1  part  for  every  10  parts  of  black  copper  lost,  and  for  antimonial 
and  arsenical  copper  2  parts  for  every  10  parts  lost. 

If  the  ore  should  contain  neither  lead,  antimony,  nor  arsenic,  a 
little  borax  is  added,  and  some  lead  during  the  fusing  process 
should  the  copper  be  very  refractory,  for  instance,  if  it  contains 
much  iron,  or  cobalt  and  nickel. 

Differences  allowed  in  assays.1 — In  the  mining  district  of  Schem- 
nitz  in  Hungary  the  assays  are  made  by  three  different  assayers. 
The  differences  allowed  in  the  results  are  as  follows  : — 

Amount  of  copper  in  ore.  Differences  allowed. 

1  to   4  per  cent.  -rf        v,?  •* - '.'  "*  .      .  0.5  per  cent. 

4  "  10       "  ;«:  .   .-,  f.r,'    .  ...  ...  0.7       " 

10  "  20  "  ,  _  V  -,  .  .  1.0  " 

20  "40  "  ,:  .  '  '.  .  V  .  2.0  " 

40  "  70  "  -.  :-:  ^.  V  '•*.""•  .  4.0  " 

70  or  more  "  .;:  3*  '...:.  6.0  " 

In  the  Klausenburg  mining  district  in  Transylvania  the  follow- 
ing differences  are  allowed  : — 

Amount  of  copper  iu  ore.  Differences  allowed. 

0  to  3.0  per  cent.  -V  '    '•*       *     -  .  0.5  per  cent. 

3.25  "    5.0       "  ,:  .; :     .    .    *     .  ...•  0.75     " 

5.25  "    8.0       "  .....  ..,,.-     *  LOO     " 

8.25  "  12.0       "  ..       .     '   .        .  1.25     " 

12.25  "  20.0       "  i        1       '.'  .     .  2.00     " 

20.25  "  40.0       "  '  ,.     -V       *tj  '  'v  3.00     " 

40.25  "  70.0       "  .        •        •    ".  4.00     " 

70.25  or  more      "  ....  6.00     " 

c.  With  lead  and  borax  (Musen  assay). — The  black  copper  ob- 
tained from  5  grammes  of  ore  is  fused  with  2.5.  grammes  of 
granulated  lead  and  a  small  quantity  of  borax.  The  muffle  is 

1  Fortschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  91.    . 


102  ASSAYING. 

slightly  opened  to  give  access  to  the  air  until  the  copper  brightens 
in  the  continually  increasing  brownish  slag.  The  dish  is  cooled 
off  in  water.  A  counter-assay  with  refined  copper  is  made,  and 
the  loss  of  copper  occurring  thereby  is  added  to  the  principal  assay. 
10  parts  of  lead  will  slag  oif  about  1  part  of  copper. — In  Mans- 
feld,  2.5  grammes  of  black  copper  were  formerly  refined  with  0.4 
grammes  of  lead. 

8»  Refining  by  cupettation. — This  method  is  the  most  suitable 
one  for  plumbiferous  black  copper,  and  especially  for  quickly 
obtaining  approximate  results.  But  a  correction  (counter-assay) 
is  necessary  to  determine  the  amount  of  copper  slagged  oif  by 
the  lead  which  becomes  oxidized  during  the  oxidizing  fusion, 
and  then  parts  with  oxygen,  not  only  to  the  foreign  metals, 
carrying  them  with  it  into  the  cupel,  but  also  slags  oif  a  part  of 
the  copper. — A  quantity  of  refined  copper,  equal  to  the  weight 
of  the  black  copper  button — for  instance,  1  to  1.25  grammes — is 
weighed  off  for  the  counter-assay.  The  assay  sample  and  the 
counter-assay  sample  are  each  wrapped  up  in  a  cornet.  A  quan- 
tity of  granulated  lead,  amounting  to.  2  or  2J  times  the  quantity 
of  copper,  is  weighed  off  for  each  copper  sample,  and  each  also 
wrapped  up  in  a  cornet.  Two  large-sized  cupels  (Fig.  54,  p.  66) 
are  placed  alongside  each  other  in  the  centre  of  the  strongly 
heated  muffle,  and  are  brought  to  a  white  heat.  Upon  each  is 
placed  one  cornet  with  lead,  and  the  mouth  of  the  muffle  is 
closed  until  the  lead  has  begun  to  "  drive"  (that  is,  until  the  dark 
film  of  lead  has  disappeared,  and  a  white  strongly  fuming  surface 
has  made  its  appearance),.  The  muffle  is  then  opened,  the  cornet 
containing  the  refined  copper  is  placed  in  one  cupel,  and  that 
containing  the  black  copper  in  the  other,  whereupon  the  muffle 
is  again  closed,  and  "driving"  is  quickly  renewed  at  a  high 
temperature.  The  mouth  of  the  furnace  is  then  slightly  opened 
to  admit  air  for  the  oxidation  of  the  lead  and  the  foreign  metals, 
the  oxides  of  which  are  absorbed  by  the  cupels,  until  the  copper 
buttons  brighten.  As  soon  as  this  has  ensued  a  spoonful  of  coal- 
dust  is  strewed  upon  the  cupels  to  prevent  the  slagging  off  of 
copper.  They  are  then  immediately  taken  out  of  the  furnace  and 
thrown  into  water.  Both  buttons  are  weighed,  and  the  loss  of 


COPPER — DRY   ASSAYS. 


103 


weight  of  refined  copper  is  added  to  the  weight  of  the  refined 
button  obtained  from  the  black  copper. 

y.  Refining  with  the  blowpipe. — 2.5  grammes  of  ore  are  roasted, 
arsenized,  and  fused  as  in  the  nickel  assay  (see  §  40).  The  but- 
ton is  weighed,  and  0.05  to  0.1  gramme  of  it  is  taken  and  fused 
with  borax  glass  upon  charcoal  in  the  inner  flame  of  the  blow- 
pipe. The  oxidizing  flame  is  then  used  until  the  dull  button  has 
become  bright ;  it  is  then  further  treated  upon  charcoal  without 
borax  in  the  reducing  flame  before  the  blowpipe  until  it  ceases  to 
fume.  The  bright  copper  button  is  weighed,  and  the  weight  cal- 
culated to  the  quantity  of  ore  used  (Rothenbach  smelting  works 
near  Mu'sen). 

2.  Oxidized  substances  without  sulphur. — These  are  fused  to 
black  copper  (p.  96)  without  being  roasted,  and  the  black  copper 
is  refined  (p.  99),  during  which  a  percentage  of  iron  will  pro- 
tect the  copper  from  slagging. 


Black 
flux. 

Antimony 
(arsenic). 

Borax. 

Glass. 

Charcoal 
dust. 

Poor  ores  with  basic  gangue 
"          "          acid         " 
"  basic  &  acid  " 
Richer  ores      .           ... 

Per  cent. 
300 
300 
300 
300 

Per  cent. 
10 
10 
12 
5  to  10 

Per  cent. 
30  to  40 
60 
30 
30  to  40 

Per  cent. 
20  to  25 
15 
30 
30  to  40 

Per  cent. 

Very  rich  ores     
Rich  sla^s       .          ... 

300 
300 

5  to  10 
5 

30  to  40 
30 

30  to  40 
30 

5  to  10 
5  to  10 

Poor  sla^s       

300 

25  to  50 

30  to  50 

15  to  20 

From  1  to  10  per  cent,  of  iron  filings  may  be  added  for  refining 
in  case  the  copper  contains  no  iron  or  other  easily  oxidizable 
metals. — The  process  of  fusing  very  poor  copper  ores  in  larger 
quantities  is  as  follows :  10  to  15  grammes  of  unroasted  ore  are 
mixed  with  15  to  20  per  cent,  of  iron  pyrites  (free  from  copper), 
and  20  per  cent,  of  sulphur,  100  per  cent,  of  borax  glass,  100  per 
cent,  of  glass,  and  20  to  25  per  cent,  of  resin  are  added,  and  a 
covering  of  common  salt.  The  charge  is  then  fused  to  matt  (matt 
assay)  in  a  clay  crucible.  The  resulting  matt  is  roasted,  etc. — 
Easily  decomposable  sulphates  (cupric  sulphate)  are  decomposed, 
before  they  are  subjected  to  the  reducing  fusion,  by  roasting  with 
an  addition  of  charcoal  (p.  33) ;  sulphate  difficult  to  decompose 


104  ASSAYING. 

(cuprous  sulphate  with  calcium  and  barium  sulphates)  by  pre- 
liminary fusion  to  matt. 

3.  Alloys  of  copper. — In  case  they  do  not  contain  too  many 
and  difficultly  oxidizable  components  (nickle,  tin,  etc.),  they  are 
refined  in  the  refinishing-dish  or  cupel ;  otherwise  the  wet  method 
of  treatment  is  preferable. 

B.  Cornish  copper  assay.1 — This  is  an  imitation  of  the  English 
smelting  process  in  the  reverberatory  furnace,  and  requires  much 
skill.  On  account  of  its  inaccurate  results  (involving  a  loss  of 
from  20  to  40  per  cent,  of  copper,  according  to  the  richness  of  the 
ore)  the  wet  method  has  been  substituted  for  it  even  in  Cornish 
smelting  works  for  valuing  ore  in  quantity.  The  following  ope- 
rations are  required  for  ores  containing  sulphur,  antimony,  or 
arsenic :  A  gentle  roasting  in  a  suitable  crucible  (Fig.  50,  p. 
64) ;  fusing  to  crude  matt  in  the  same  crucible.  This  is  then 
roasted,  and  the  roasted  assay  sample  is  fused  to  black  copper. 
This  is  purified  by  fusing  it  with  oxidizing  and  solvent  agents, 
and  the  purified  black  copper  is  refined  with  oxidizing  and  solvent 
agents,  and  finally  the  slag  is  fused.  All  operations  are  carried 
out  in  the  Cornish  clay  crucibles  (Fig.  50,  p.  64.). 

29.    WET   ASSAYS.2 

These,  on  account  of  their  greater  accuracy  and  simpler  execu- 
tion, have,  as  a  general  rule,  been  substituted  for  dry  assays.  The 
choice  of  one  of  the  numerous  wet  assays  depends  chiefly  on  the 
foreign  admixtures  (antimony,  arsenic,  lead,  bismuth,  mercury, 
etc.),  and  somewhat  on  the  richness  of  the  sample.  Colorimetric 
assays  are  especially  adapted  for  poorer  ores,  and  volumetric  assays, 
if  many  are  to  be  made  in  quick  succession,  are  preferred  to  gra- 
vimetric assays. 

A.  Gravimetric  assays. — The  methods  by  which  the  copper  is 
determined  in  the  metallic  state  (Swedish  and  electrolytic  assay) 
are  simpler  and  more  convenient  to  execute  than  those  by  wThich 

['  Percy's  Metallurgy  of  Copper,  Zinc,  and  Brass,  pp.  454-478. — G.] 

[2  Comparison  of  Various  Methods  of  Copper  Analysis.     W.  E.  C.  Eustis, 

Boston,  Mass.,  Trans.  American  Institute  of  Mining  Engineers,  vol.  xi.  pp. 

120-135.— G.] 


COPPER — WET   ASSAYS.  105 

the  copper  is  separated  and  determined  in  combination  (determi- 
nation of  copper  as  cuprous  sulphide,  or  as  subsulphocyanide). 
The  Swedish  assay  can  be  executed  in  less  time  than  the  electro- 
lytic assay,  but  it  is  done  at  the  expense  of  accuracy,  especially 
with  poorer  ores. 

1.  Modified  Swedish  assay.1  —  The  cupriferous  substance  is 
brought  into  solution  with  sulphuric  or  hydrochloric  acid  (nitric 
acid  must  not  be  used,  as  the  precipitated  copper  is  again  dis- 
solved in  it),  and  the  copper  precipitated  with  iron  or  zinc,  and 
determined  either  as  metal  or  oxide.  This  plan  is  not  admissible 
in  the  presence  of  metals,  which  are  also  precipitated  by  iron  and 
zinc. 

But  such  metals  can  be  removed  during  the  operation  without 
injurious  effect  (lead  or  sulphate,  silver  as  silver  chloride,  mercury 
by  igniting  the  precipitated  copper) ;  or  they  must  be  removed 
by  a  preparatory  operation  (arsenic  by  roasting  the  assay  sample 
with  charcoal  powder),  or  first  by  itself,  and  then  with  an  addition 
of  some  iron  pyrites  at  not  too  high  a  temperature ;  tin  and  anti- 
mony by  heating  with  moderately  diluted  sulphuric  acid,  then 
adding  nitric  acid,  and  heating  nearly  to  boiling,  and  an  addi- 
tion, if  necessary,  as  in  the  case  of  metallic  sulphides,  of  a  few 
drops  of  fuming  nitric  acid.  The  solution  is  then  evaporated  to 
dryness  until  the  fuming  ceases.  The  dry  mass  is  dissolved  in 
hot  water  and  filtered,  and  the  solution  treated  with  some  hydro- 
chloric or  nitric  acid,  etc. ;  or,  the  antimony  is  removed  by  fusing 
the  assay  sample  with  potassium  hydrate  or  potassium  carbonate 
in  a  silver  crucible,  lixiviating  the  potassium  antimoniate,  and 
dissolving  the  residue ;  or,  the  assay  sample  is  dissolved,  neu- 
tralized with  soda,  and  digested  with  a  solution  of  sodium  sul- 
phide to  extract  the  antimony,  arsenic,  and  tin  in  soluble  form. 
It  is  now  filtered,  and  the  residue  washed  and  dissolved  as  above. 
To  separate  bismuth  by  analytical  methods  is  a  very  tedious 
operation.  Ores  containing  bitumen,  for  instance  cupriferous 
schists  (Kupferschiefer),  must  be  ignited  to  remove  the  bitumen, 
before  they  are  dissolved.  Impure  (black)  precipitated  copper 
can  be  further  examined  according  to  Parkers  and  Fleitmann's 
volumetric  method  to  be  shortly  described. 

i  B.  u.  h.  Ztg.  1869,  p.  12. 


106  ASSAYING. 

a.  Precipitation  with  iron. — 1  to  5  grammes,  according  to  de- 
gree of  richness  of  copper ;  generally,  2.5  to  5  grammes  of  the 
assay  sample  are  decomposed  in  a  suitable  flask  (Fig.  10,  p.  36), 
which  is  placed  in  an  oblique  position,  by  heating  with  sulphuric 
acid,  and  adding  from  time  to  time  some  fuming  nitric  acid,  or 
potassium  chlorate,  until  the  separated  sulphur,  inclosing  parti- 
cles of  the  ore,  is  oxidized  as  much  as  possible ;  or,  the  sample  is 
at  once  dissolved  in  aqua  regia  (see  also  p.  36  for  method  of  de- 
composing metallic  sulphides).  It  is  now  evaporated  to  dryness 
with  some  sulphuric  acid,  or  until  the  sulphuric  acid  vapors  ap- 
pear in  the  flask.  A  few  drops  of  sulphuric  acid  are  added  to 
the  dry  mass  (to  dissolve  the  basic  salts),  and  then  water  is  cau- 
tiously added  ;  or,  is  at  once  added  to  the  (cooled  off)  mass,  while 
it  still  contains  free  acid.  The  fluid  now  entirely  free  from  nitric 
acid  is  filtered  into  a  glass  flask,  such  as  is  shown  in  Fig.  16,  p. 
39.  The  residue  is  washed  until  the  wash-water  no  longer  pro- 
duces a  red  slain  upon  a  piece  of  bright  sheet  iron.  Two  pieces 
of  iron  wire,  3  to  4  centimeters  long,  are  then  added  (or,  in  order 
to  shorten  the  time  required  for  the  assay,  the  fluid  may  at  once 
be  filtered  into  a  porcelain  dish  in  which  the  iron  wires  lie,  and 
copper  will  then  be  precipitated  during  the  filtration).  The  fil- 
trate is  sufficiently  diluted  and  gently  heated  until  a  pointed  iron 
wire,  when  dipped  into  the  fluid,  shows  no  reddish  stain  of  cop- 
per. The  copper  is  twice  decanted  with  cold  water  into  a  spacious 
beaker-glass  (to  prevent  the  separation  of  basic  iron  salts,  which 
are  more  easily  formed  by  hot  water),  and  is  then  decanted  three 
times  with  boiling  water.  The  flask  is  now  completely  filled 
with  cold  water  ;  a  flat-bottomed  porcelain  dish,  about  80  milli- 
meters wide  and  20  millimeters  high,  is  placed  bottom  upwards 
on  top  of  it.  The  flask  and  dish  are  then  inverted.  The  mouth 
of  the  flask  is  held  in  an  oblique  position^  and  the  water  is  al- 
lowed to  run  into  the  dish  until  it  is  nearly  full.  The  flask  is 
left  standing  in  the  dish  until  all  the  copper  and  the  iron  wires 
have  fallen  into  the  water  in  the  dish  (small  particles  of  carbon 
separated  from  the  iron  will  remain  floating  on  the  water  for 
some  time).  The  flask  is  now  quietly  drawn  over  the  side  of  the 
dish,  which  should  be  somewhat  inclined  for  the  purpose.  The 
iron  is  freed  from  copper  by  rubbing  with  the  fingers,  which 


COPPER- — WET   ASSAYS.  107 

should  be  rinsed  off  in  the  water.  The  copper  is  now  decanted 
twice  with  boiling  water.  This  is  poured  off  as  completely  as 
possible  from  the  copper,  which  is  moistened  with  absolute  alco- 
hol, and  dried  on  the  water-bath,  until  it  has  assumed  a  pulve- 
rulent condition.  It  is  allowed  to  cool  in  the  desiccator,  and  is 
then  brought  upon  the  pan  of  the  balance,  or  into  a  tared  por- 
celain crucible  with  the  aid  of  a  fine  brush,  and  quickly  weighed. 
It  is  now  dried  for  10  or  15  minutes  more,  and  again  weighed 
until  the  results  agree ;  or  the  copper  is  spread  out  upon  a  roast- 
ing dish  and  ignited  in  the  muffle-furnace,  and  the  metal  calcu- 
lated from  the  amount  of  cupric  oxide  formed  (100  cupric  oxide 
=  79.88  copper).  If  the  water  used  in  decantation  shows  a 
reddish  sediment  in  the  beaker-glass,  it  should  be  filtered,  the 
filter  dried  and  ignited  upon  the  scorifier,  and  the  percentage  of 
copper  resulting  from  the  cupric  oxide  should  be  added  to  the 
principal  yield. 

Correction  for  iron  that  may  be  contained  in  the  precipitated 
copper  on  account  of  a  deposit  of  basic  iron  salts  :  The  precipi- 
tated copper  is  ignited  upon  the  scorifier  until  it  becomes  black. 
The  cupric  and  ferric  oxides  formed  are  weighed  and  dissolved 
in  hydrochloric  or  sulphuric  acid.  The  ferric  oxide  is  precipi- 
tated with  ammonia.  The  solution  is  filtered  upon  a  small  filter 
of  paper.  The  filter  is  dried  and  ignited,  and  the  ferric  oxide, 
which  may  be  found,  is  deducted  from  the  combined  weight  of 
the  cupric  and  ferric  oxides,  and  the  copper  calculated  from  the 
quantity  of  pure  cupric  oxide  found.  Instead  of  decanting  the 
precipitated  copper,  it  may  all  be  filtered,  dried,  ignited,  weighed, 
and  dissolved,  as  above,  for  obtaining  the  percentage  of  iron. 

Pure  precipitated  copper  has  a  fine  copper  color.  If  the  solu- 
tion contains  antimony  and  arsenic,  it  has  first  a  copper  color, 
which  changes  to  black,  by  the  antimony  and  arsenic  which  are 
precipitated  later  on.  The  largest  portion  of  the  antimony,  after 
the  precipitate  has  been  evaporated  to  dry  ness  with  sulphuric 
acid  and  again  moistened  with  water,  remains  as  basic  sulphate 
of  antimony,  while  arsenic  passes  into  solution.  The  residue 
from  the  solution  of  the  ore,  etc.,  is  tested  for  copper  by  heating 
it  with  nitric  acid,  filtering,  and  adding  ammonia  in  excess 
(appearance  of  a  blue  color  indicates  copper.) 


108  ASSAYING. 

Instead  of  two  iron  wires,  a  simple  one,  bent  into  the  form  of 
a  ring  with  one  end  projecting  vertically,  may  be  used.  The 
ring  is  dipped  into  the  liquid  contained  in  a  beaker-glass  in  such 
a  manner  that  the  end  projects.  "When  the  precipitation  is  com- 
plete the  copper  is. rinsed  from  the  ring,  decanted,  etc.,  as  above. — 
Or  a  strip  of  sheet-iron  may  be  used  instead  of  the  wire,  but  it 
must  be  immediately  removed  from  the  liquid  after  the  precipi- 
tation of  the  copper  is  complete  to  avoid  the  formation  of  basic 
iron  salts.  In  solutions  that  are  too  concentrated  the  copper 
adheres  too  strongly  to  the  iron. 

b.  Precipitation  with  zino  free  from  lead  and  arsenic.1 — A  solu- 
tion of  the  assay  sample  is  prepared  with  sulphuric  acid,  as 
described  on  p.  106,  and  filtered.  A  strip  of  zinc  is  placed  in  it, 
and  the  solution  is  then  heated  until  a  bright  iron  wire  held  into 
it  shows  no  copper  deposit ;  or  until  a  drop  of  the  solution  placed 
upon  a  porcelain  dish  is  not  browned  by  sulphuretted  hydrogen. 
The  strip  of  zinc  is  then  taken  out,  and  the  precipitated  copper 
is  washed  off  with  the  wash-bottle.  It  is  filtered,  until  but  a 
small  layer  of  water  covering  the  copper  remains.  A  few  drops 
of  warm  hydrochloric  acid  are  then  added  to  dissolve  any  particles 
of  zinc  which  may  be  present.  It  is  now  decanted,  etc.,  as  in 
the  precipitation  with  iron  (p.  106) ;  or  it  is  filtered  as  soon  as 
effervescence  has  ceased,  quickly  washed  with  hot  water,  and 
dried.  The  copper  is  then  detached  from  the  filter,  ignited  on 
the  cover  of  a  porcelain  or  platinum  crucible,  or  upon  a  roasting 
dish  in  the  muffle,  and  the  oxide  quickly  weighed.  The  black 
crust  upon  the  end  of  the  piece  of  zinc,  which  has  been  dipped 
into  fluid,  is  a  spongy  layer  of  zinc  colored  by  a  trace  of  sulphide 
of  copper.  Nickel,  which  is  not  thrown  down  by  iron,  is  precipi- 
tated with  zinc,  but  cobalt  is  not. 

Granulated  zinc  may  be  used  instead  of  a  strip,  but  the  gran- 
ules must  be  completely  dissolved  by  the  time  the  bubbles  cease. 
The  copper  is  then  decanted,  etc.  The  cuprous  fluid  may  be  fil- 
tered into  a  platinum  dish,  and  some  hydrochloric  acid  added  to 
it.  It  is  then  heated,  and  a  few  small  pieces  of  zinc  added  to  it, 

1  Fresenius's  Ztschr.  fur  analyt.  Cliemie  iii.  334  (Mohr  und  Fresenius). 
Oest.  Ztschr.  1868,  No.  48  (von  Kripp).  Erdmann's  J.  f.  pr.  Chemie,  cii.  477 
(Ullgreen).  Darstellung  von  pulverformigein  Zinke  in  Dingier,  ccxxviii.  378. 


COPPER — WET   ASSAYS.  109 

whereupon  the  copper  will  deposit  itself,  firmly  on  the  platinum, 
but  loosely  on  the  zinc.  After  precipitation  is  complete,  which 
fact  is  to  be  tested  with  sulphuretted  hydrogen,  as  above,  the  cop- 
per is  rubbed  and  washed  off  from  the  zinc.  It  is  then  allowed 
to  settle,  is  decanted,  treated  with  hot  water,  to  which  some  hy- 
drochloric acid  had  been  added ;  then  quickly  washed  with  hot 
water  by  decantation  to  prevent  the  loss  of  any  of  the  copper  by 
solution.  It  is  finally  moistened  with  some  absolute  alcohol, 
dried  in  a  water-bath,  or  at  110°  to  120°  C.  (230°  to  248°  Fahr.), 
and  the  tared  platinum  dish,  which  has  been  allowed  to  cool  off 
in  the  desiccator,  is  weighed ;  or  the  copper,  if  the  utmost  accu- 
racy is  demanded,  is  heated  in  a  stream  of  sulphuretted  hydrogen. 
— Cuprous  schist  (Kupferschiefer)  i1  5  grammes  are  heated  with 
40  to  50  cubic  centimeters  of  hydrochloric  acid.  When  the  car- 
bonic acid  has  been  expelled,  6  cubic  centimeters  of  diluted  acid, 
consisting  of  equal  parts  of  nitric  acid,  of  1.2  specific  gravity,  and 
water,  are  added  (to  ores  free  from  bitumen,  or  which  have  been 
ignited,  1  cubic  centimeter  of  nitric  acid).  This  is  digested  for 
half  an  hour,  then  boiled  for  a  quarter  of  an  hour.  The  hot 
liquid,  which  should  contain  no  free  nitric  acid,  is  filtered  into  a 
beaker-glass.  A  small  rod  of  zinc  upon  a  strip  of  platinum  is 
placed  in  the  filtrate,  and  the  copper  is  precipitated,  which  will 
require  from  J  to  f  of  an  hour.  The  precipitated  copper  is  then 
decanted  and  dissolved  in  nitric  acid,  together  with  that  adhering 
to  the  platinum,  and  titrated  with  a  solution  of  potassium  cyanide 
(seep.  122). 

The  following  gravimetric  method  for  the  determination  of  cop- 
per is  recommended  by  Genth  as  giving  very  accurate  results  when 
proper  care  has  been  taken  that  nothing  is  lost  in  dissolving  the 
ore  and  in  the  evaporation:  The  finely-powdered  ore  is  placed 
in  a  small  beaker,  and  enough  pure  H2S04  added  to  convert  all 
metals  present  into  sulphates  and  to  drive  off  all  the  HN03,  which 
is  used  for  dissolving.  The  nearly  dry  mass,  after  giving  off  copi- 
ous fumes  of  S03,  is  allowed  to  cool,  and  dissolved  in  a  small  quan- 
tity of  water,  when  all,  excepting  quartz,  etc.,  is  in  solution,  the  trace 
of  Ag  which  may  be  present  is  precipitated  by  a  drop  of  HC1,  when 
the  liquid  is  clear,  the  insoluble  silicates,  PbS04,  AgCl,  and  the 

1  Fresenius's  Ztschr.  viii.  9. 


110  ASSAYING. 

greater  part  of  the  antimoniate  of  antimony,  are  separated  by  filtra- 
tion from  the  Cu,  As,  etc.  The  clear  liquid  is  next  precipitated  by 
H2S,  which  throws  down  CuS,  and  traces  of  Sb2S3  and  As2S3 — (the 
greater  part  of  the  As  remains  in  solution  as  As205),  as  but  a  small 
amount  is  reduced  to  As203,  and  precipitated  by  the  H2S).  The  CuS 
is  washed,  then  treated  with  K2S  to  dissolve  the  Sb2S3  and  As2S3, 
which  may  have  come  down,  and,  after  washing,  boiled  with  strong 
HC1  to  dissolve  any  ZnS  which  may  have  been  precipitated  with  the 
CuS,  then  diluted  with  boiling  water,  and  a  sufficient  quantity  of  H2S 
is  added  to  precipitate  any  traces  of  Cu  which  may  have  gone  into 
solution.  The  CuS  is  washed,  dried,  carefully  roasted,  then  dis- 
solved with  2  or  3  drops  of  H.2S04,  H2O,  and  HNO3.  After  every- 
thing is  in  solution  the  latter  is  evaporated  to  dryness,  carefully 
heated,  and  finally  ignited  to  drive  off  every  trace  of  H2S04,  and 
from  the  resulting  CuO  the  amount  of  Cu  is  calculated. 

2.  Electrolytic  assays.1 — The  copper  is  precipitated  in  a  cohe- 
rent film  upon  a  weighed  platinum  strip  by  the  galvanic  current, 
from  the  solution  of  the  nitrate  containing  free  nitric  acid,  which 
need  not  be  filtered.  From  this  solution,  zinc,  iron,  nickel,  cobalt, 
and  chromium  are  not  precipitated  by  galvanic  action.  The  fol- 
lowing are  precipitated  in  the  form  of  peroxides  at  the  positive 
electrode  :  namely,  lead,  manganese,  and  (partially)  silver.  Mer- 
cury is  precipitated  at  the  negative  electrode  in  the  metallic  state 
before  copper ;  silver  and  bismuth  at  the  same  time  as  copper,  and 
selenium,  antimony,  and  arsenic2  only  a  considerable  time  later ; 
the  assay,  therefore,  as  a  general  rule,  requires  the  absence  of  the 
last-named  metals  and  metalloids,  which  blacken  the  fine  red 
color  of  the  copper.  Antimony  remains  behind  undissolved, 
when  the  assay  sample  is  dissolved  in  nitric  acid.  A  large  num- 
ber of  assays  can  be  carried  out  at  the  same  time  according  to 

1  Fresenius's  Ztschr.  iii.  334  ;  vii.  253  ;  ix.  102.     B.  u.  h.  Ztg.  1869,  p.  43, 
181 ;  1872,  p.  251  ;  1875,  p.  155  ;  1877,  pp.  5,  32.     Preuss.  Ztschr.  xvii.  Lief. 
3;  xx.  Lief.  1.     Grothe,  polyt.  Ztschr.  1877,  p.  11.     The  Electrolytic  Deter- 
mination of  Copper,  and  the  Formation  and  Composition  of  so-called  Allotro- 
pic  Copper.  J.  B.  Mackintosh,  Trans.  Am.  Inst.  Mining  Engineers,  vol.  x.  p.  57. 

2  [According  to  Eustis  in  sulphate  and  nitrate  solutions,  containing  50  per 
cent,  arsenious  oxide  in  solution,  no  arsenic  is  precipitated  as  long  as  an  insol- 
uble electrode  is  used.     Trans.  Am.  Inst.  M.  E.  vol.  xi.  p.  124. — G.] 


COPPER — WET   ASSAYS. 


Ill 


this  very  accurate  and  simple  method,  which  is  adapted  for  rich 
as  well  as  poor  ores,  etc. 

It  is  best  to  employ  for  the  galvanic  current,  the  Meidinger- 
Pinkus's  battery1  (with  6  large  elements  for  richer  copper  ores, 
and  4  small  elements  for  poor  ores  with  less  than  10  per  cent. 
Cu)  ;  or  Clamond's  thermo-electric  battery2  (consisting  of  a  number 
of  zinc  and  antimony  elements  arranged  in  the  form  of  a  ring, 
and  heated  by  a  gas-flame)  may  be  used.  If  the  current  is  too 
strong,  the  copper  does  not  deposit  itself  firmly  upon  the  plati- 
num. The  copper  is  not  precipitated  in  as  pure  and  coherent  a 
state,  from  the  solution  of  the  sulphate  containing  free  sulphuric 
acid,  and  in  case  iron  should  be  present  a  part  of  this  is  thrown 
down  with  the  copper,  while  another  part  is  reduced  to  protoxide. 

One  gramme  of  the  assay  sample  is  dissolved  in  strong  nitric 
acid  and  evaporated  to  dryness  in  a  porcelain  dish.  If  necessary, 
the  dish  is  heated  over  a  lamp  to  burn  off  any  separated  sulphur 
(p.  36).  The  residuum  is  dissolved  in  20  cubic  centimeters  of 
nitric  acid  of  1.2  sp.  gr.,  and  filtered  into  a  beaker-glass.  The 
filtrate  is  diluted  to  180  to  200  cubic  centimeters,  and  stirred. 
The  platinum  spiral  a  (Fig.  66),  weighing  about  16  grammes, 
is  now  placed  in  the  beaker-glass.  A 
cone  of  platinum  foil  (Fig.  65),  weigh- 
ing about  20  grammes,  is  suspended 
over  this  from  a  stand  in  such  a  manner 
that,  when  rich  ores  are  to  be  tested,  the 
cone  hangs,  at  the  utmost,  1  centimeter 
above  the  foot  ring  b  of  the  spiral,  but 
only  0.5  centimeter  in  case  of  poorer 
ores,  and  that  a  part  of  the  cone  shall 
project  above  the  liquid.  The  cone  is 
connected  by  means  of  a  wire  conductor  with  the  negative  electrode, 
and  the  spiral  with  the  positive.  The  beaker-glass  should  be 
covered  with  a  glass  plate,  cut  into  halves,  and  each  half  per- 
forated with  a  hole  for  the  wires  to  pass  through.  The  strength 
of  the  galvanic  current  used  is  generally  such  that  90  to  100 


Fig.  65. 


Fig.  66. 


1  Fresenius's  Ztschr.  xi.  4  (Mansfeld). 

2  B.  u.  h.  Ztg.  1875,  pp.  155,  251,  303. 


112  ASSAYING. 

cubic  centimeters  of  water-gas  will  be  developed  in  30  minutes 
in  the  voltameter  from  diluted  sulphuric  acid  (1  :  12),  and  as 
much  as  180  cubic  centimeters  from  rich  cupriferous  substances. 
After  an  electrolytic  action  of  12  to  18  hours  the  liquid  is  ex- 
amined in  order  to  ascertain  whether  the  whole  of  the  copper  has 
been  precipitated,  by  adding  some  water,  and  stirring.1  In  case 
it  still  contains  copper,  the  bright  portion  of  the  platinum  cone, 
now  partly  submerged,  will  be  covered  with  a  red  film  of  copper. 
If  no  more  copper  is  separated,  the  beaker-glass  is  placed  in  a 
spacious  porcelain  dish,  and  the  acid  liquid  it  contains  is  dis- 
placed by  adding  water  until  all  acid  reaction  disappears  (or  the 
liquid  is  removed  with  a  siphon,  and  water  is  added  from  a  wash- 
bottle  until  gas  ceases  to  develop  at  the  positive  electrode).  The 
cone  of  platinum  is  then  taken  out  and  placed  in  a  beaker-glass 
with  water.  It  is  then  rinsed  off  with  hot  water,  next  placed  in  a 
beaker-glass  filled  with  absolute  alcohol,  or  washed  with  it,  and 
finally  laid  upon  blotting  paper,  and  dried  in  an  air-bath  at  about 
94°  C.  (201.2°  Fahr.).  (If  the  operator  has  some  experience,  this 
can  be  done  more  quickly  upon  a  piece  of  sheet-iron  heated  over  a 
lamp,  or  by  holding  the  cone  in  the  hot  air  arising  from  a  large 
platinum  or  silver  dish  heated  by  the  flame.)  After  it  has  cooled 
oif  the  cone  is  weighed ;  and,  as  its  weight  had  been  accurately 
ascertained  before  the  operation,  the  weight  of  the  copper  will  be 
given  by  the  increase  in  weight  of  the  cone,  from  which  the 
copper  can  then  be  dissolved  by  hot  nitric  acid.  Dark  spots 
upon  the  red  copper  indicate  the  presence  of  arsenic,  antimony,  or 
selenium.  If  only  small  quantities  of  the  first  two  are  present, 
they  are  very  slowly  precipitated,  or  not  at  all,  from  a  strong  acid 
solution,  if  the  current  is  interrupted,  while  the  fluid  possesses 
still  a  faint  bluish  color.  The  presence  of  much  iron  prevents  a 
complete  precipitation  of  the  copper,  as  it  (Cu)  is  dissolved  by 
the  ferric  sulphate  while  ferrous  oxide  is  formed,  the  action  of 
free  nitric  acid  upon  which  produces  blackish-brown  circles 
around  the  platinum  cone.  When  this  is  observed  it  is  a  sure 

[J  If  the  solution  is  heated  and  maintained  at  a  temperature  of  from  70°  to 
80°  C.  during  the  reaction,  this  period  may  be  shortened  to  4  or  5  hours. 
The  strength  of  the  current  under  these  circumstances  can  be  reduced  to  one. 
Bunsen  Cell.  (Classen  Ber.  d.  ch.  ges.  18.  1796.)— Gr.] 


COPPER — WET   ASSAYS. 


113 


Fig.  67. 


indication  that  the  process  of  precipitating  the  copper  has  not 
taken  place  properly.  In  this  case  the  assay  sample  is  dissolved 
in  40  cubic  centimeters  of  nitric  acid,  and  360  cubic  centimeters 
of  water,  using  a  stronger  galvanic  current,  giving  120  cubic 
centimeters  of  water-gases  in  Volta's  apparatus ;  or,  what  is  still 
better,  the  copper  is  precipitated  from  an  acid  solution  by  sul- 
phuretted hydrogen,  and  the  copper  sulphide  dissolved  in  30 
cubic  centimeters  of  nitric  acid  of  1.2  specific  gravity.  It  is  then 
digested  until  the  sulphur  shows  yellow.  200  cubic  centimeters 
of  water  are  added,  the  fluid  is  then  electrolyzed. 

Hwpmt  dissolves  1  gramme  or  more  of  the  assay  sample  in 
nitric  acid,  evaporates  nearly  to  dryness,  dissolves  in  a  small 
quantity  of  dilute  sulphuric  acid,  and  dilutes  the  solution  to  60 
or  70  cubic  centimeters.  The  solution  is  poured  into  the  plati- 
num dish  A  (Fig.  67),  and  the  conducting 
stand  B  of  the  dish  is  connected  with  the 
negative  electrode,  the  platinum  spiral  C 
with  the  positive  electrode,  and  the  liquid 
electrolyzed  after  the  funnel  D  has  been 
placed  in  position.  When  the  copper  has 
been  precipitated,  the  fluid  is  poured  from 
the  dish.  This  is  rinsed  out  first  with 
water,  and  next  with  alcohol,  then  dried 
and  weighed,  the  copper  being  determined 
from  the  increase  of  weight. — Hampe's2 

method    of   testing    refined    copper:    25         I 1 

grammes   of   copper   are   dissolved   in  a 

beaker,  at  a  moderate  temperature,  in  200  cubic  centimeters  of 
water,  and  175  to  180  cubic  centimeters  of  nitric  acid  of  1.2 
specific  gravity.  To  this  are  added  25  grammes  of  previously 
diluted  sulphuric  acid  (about  4  cubic  centimeters  more  than  is  re- 
quired for  transforming  the  nitrate  into  sulphate).  The  liquid  is 
then  evaporated  to  dryness  in  a  porcelain  dish  on  the  water-bath. 
The  dry  mass  is  heated  upon  a  sand-bath  until  the  volatilization 
of  the  free  sulphuric  acid  is  complete.  The  dish  is  then  covered, 
and,  after  the  mass  has  become  cool,  20  cubic  centimeters  of  nitric 

1  B.  n.  h.  Ztg.  1875,  p.  394.     Dingier,  ccxvii.  440. 

2  Preuss.  Ztschr.  xxi.  Lief.  5.     Fresenius's  Ztscbr.  xiii.  176. 
8 


114  ASSAYING. 

acid  are  added  to  it.  Water  is  now  allowed  to  flow  gradually 
into  the  dish  until  the  entire  volume  amounts  to  350  cubic  centi- 
meters. The  silver  is  removed  by  the  addition  of  an  equivalent 
quantity  of  hydrochloric  acid.  The  liquid  is  electrolyzed  in  a 
vessel  capable  of  holding  from  400  to  450  cubic  centimeters. 
The  strength  of  the  galvanic  current  used  should  be  such  that 
130  cubic  centimeters  of  oxy hydrogen  gas — it  may  vary  from 
90  to  180  cubic  centimeters — are  developed  in  30  minutes  in  the 
voltameter  from  diluted  sulphuric  acid  (1  :  12).  The  liquid  is 
electrolyzed  for  about  72  hours,  the  subsequent  manipulations 
being  the  same  as  above  described. — The  presence  of  small  quan- 
tities of  bismuth  in  the  precipitated  copper  can  be  determined 
by  the  following  process  :  The  copper  is  dissolved  in  nitric  acid, 
concentrated  hydrochloric  acid  in  large  excess  is  added,  and  the 
nitric  acid  boiled  away.  The  excess  of  hydrochloric  acid  is 
evaporated  on  the  water-bath,  a  large  quantity  of  boiling  water 
is  added,  and,  after  24  hours,  the  precipitate,  .consisting  of  basic 
bismuth  and  copper  salts,  is  filtered  off.  The  filtrate  is  dissolved 
in  hydrochloric  acid,  and  again  precipitated  with  water.  This 
precipitate  is  dissolved  in  nitric  acid,  and  the  copper  contained 
therein  separated  by  ammonium  carbonate. 

Classen's1  method  for  the  electrolytic  determination  of  metals  is 
much  used,  and  is  based  upon  the  fact  that  the  separation  of  the 
metal  is  best  effected  when  the  oxide  is  fixed  to  an  acid  readily  de- 
composed by  the  current,  so  that  a  secondary  reaction  cannot  take 
place.  Such  an  acid  is  oxalic  acid,  which  splits  into  carbonic  acid 
and  hydrogen.  Most  heavy  metals  give  insoluble  precipitates  with 
oxalic  acid ;  their  double  alkaline  salts  are,  however,  readily  soluble, 
and  by  adding  ammonium  oxalate  in  excess  the  reaction  progresses 
with  ease  and  without  the  formation  of  a  precipitate.  The  carbonic 
acid  separated  on  the  positive  pole  by  the  decomposition  of  the  am- 
monium oxalate  combines  with  the  ammonium  forming  ammonium 
carbonate.  In  general  the  process  is  conducted  by  converting  the 
neutral  chlorides  and  sulphates  of  the  metals  into  double  oxalates 
by  the  addition  of  a  large  excess  of  ammonium  oxalate,  heating  the 
solution  and  exposing  it  to  the  action  of  a  galvanic  current  whereby 
the  metals  deposit  quickly  and  in  a  compact  form  on  the  negative 
electrode. 

1  "  Quantitat.  Analyse  auf  elektrolytischem,  Wege."     Aachen,  1885. 


COPPER — WET  ASSAYS. 


115 


The  determination  of  copper,  as  is  well  known,  can  be  very 
easily  effected  directly  from  the  acid  solution.  According  to  Classen's 
method  the  solution  (concentrated,  if  necessary,  by  evaporation) 

Fig.  68. 


is  heated  to  boiling,  and,  after  adding  3  to  4 
grammes  of  solid  ammonium  oxalate,  subjected  to 
the  action  of  the  electric  current  as  soon  as  every- 
thing is  dissolved.  The  copper  separates  quickly 
and  easily,  provided  the  current  is  not  too  weak. 
With  a  strength  of  current  corresponding  to 
300  c.c.  of  oxy hydrogen  gas  per  hour,  0.15 
gramme  of  metallic  copper  can  be  separated  in  25 
minutes.  As  the  negative  electrode,  Classen  uses 
a  platinum  dish,  and  for  the  positive  electrode  a 
disk  4  to  5  centimeters  in  diameter  of  moderately 
thick  platinum  sheet  (Fig.  69),  which  is  secured 
by  a  screw  to  a  medium  thick  platinum  wire. 
To  prevent  loss,  the  platinum  dish  is  covered 
with  a  watch  crystal  perforated  in  the  centre. 
The  entire  arrangement  of  the  apparatus  is  shown 
in  Fig.  68.  The  glass  cylinder  shown  in  front 
is  the  resistance  arrangement  recommended  by 
Classen  for  the  reduction  of  more  considerable 
strengths  of  current.  It  consists  of  a  rod  6  with 


Fig.  69. 


116  ASSAYING. 

a  zinc  pole,  which  can  be  moved  to  and  from  the  zinc  pole  a  until 
the  current  reaches  the  desired  strength.  The  zinc  plates  (poles) 
must  be  amalgamated  with  mercury  and  hydrochloric  acid,  and  the 
contacts  at  a,  &,*kept  clean. 

As  recently  precipitated  sulphide.1 — When  copper  is  met  with  in 
the  course  of  analysis  as  recently  precipitated  sulphide,  it  should 
be  dissolved  in  potassium  cyanide,  and  the  warm  solution  (70°  C.), 
after  adding  excess  of  ammonium  carbonate,  electrolytically  decom- 
posed. The  deposit  is  exceedingly  rapid  and  perfect. 

3.  Determination  of  the  copper  in  the  form  of  cuprous  sul- 
phide.2— This  demands  the  absence  of  metals  precipitable  from 
acid  solutions  with  sulphuretted  hydrogen,  and  the  metallic  sul- 
phides of  which  are  not  volatilized  in  a  heated  current  of  hy- 
drogen (silver^  lead,  bismuth, .  cadmium,  antimony,  tin).  During 
the  dissolving  process,  lead  may  be  separated  by  sulphuric  acid, 
antimony  and  tin  by  nitric  acid ;  mercury  and  arsenic  sulphide  are 
volatile.  In  case  a  considerable  percentage  of  nickel  is  present, 
nickel  sulphide  will  be  precipitated  with  sulphuretted  hydrogen, 
which  can  only  be  prevented  by  using  a  large  excess  of  acid. 

One  to  5  grammes  of  the  assay  sample  are  decomposed  with  nitric 
acid  or  aqua  regia.  The  residue  of  sulphur  is  removed  by  hydro- 
chloric acid  and  potassium  chlorate.  The  liquid  is  then  diluted 
with  water  and  the  silver  precipitated  with  common  salt.  The 
solution  is  then  filtered,  heated  to  about  80°  to  100°  G.  (176°  to 
212°  F.),  and  saturated  with  sulphuretted  hydrogen,  the  precipi- 
tate filtered,  after  standing  about  one  hour,  and  quickly  washed 
with  hot  water.  The  filter  is  dried  between  blotting  paper  and 
next  quickly  in  a  hot  sand-bath.  The  precipitate  is  detached 
from  it  and  the  filter  with  the  addition  of  some  sulphur  incine- 
rated upon  the  cover  of  a  tarred  porcelain  evaporating  dish  which 
contains  the  copper  sulphide.  This,  after  an  addition  of  sulphur, 
is  strongly  heated  for  about  half  an  hour,  while  a  current  of  hy- 
drogen or  illuminating  gas  is  conducted  to  it  through  an  opening 
in  the  cover,  or  through  a  perforated  mica  plate,  which  has  been 
placed  upon  the  crucible.  Cu2S  with  79.85  per  cent,  of  copper 

1  Chem.  News,  1886,  p.  209. 

2  Bestimmung  des   Kupfers   in    kupferhaltigen    Kiesen,   Abbr.auden    und 
ausgelaugten  Abbranden  in  Fresenius's  Ztschr.  xvi.  335. 


COPPER — WET  ASSAYS. 


117 


will  be  formed.  (If  a  current  of  carbonic  acid  is  used,  too  much 
Cu2S  is  obtained,  in  consequence  of  the  less  complete  decomposi- 
tion of  the  cupric  sulphide.) 

Of  nickel  coins,  0.5  grammes  are  dissolved  in  nitric  acid  and 
evaporated  to  dry  ness  with  1  cubic  centimeter  of  sulphuric  acid, 
the  residue  is  dissolved  in  200  cubic  centimeters  of  boiling  water, 
and  the  solution  precipitated  with  sulphuretted  hydrogen,  etc. 

Apparatus1  for  igniting  in  a  current  of  hydrogen  (Fig.  70). — 
a,  a  vessel  with  water  and  zinc ;  6,  funnel  for  pouring  in  sulphuric 
acid ;  c,  discharge-pipe  for  the  gas ;  d,  drying  tube  for  the  calcium 

Fig.  70. 


chloride ;  e,  gas  discharge-pipe ;  g,  porcelain  crucible  with  perfo- 
rated cover  (Rose's  crucible) ;  I,  lamp.     Fig.  71 — a,  gas  generating 

Fig.  71. 


flask   with   funnel  tube  b ;    c,   wash  vessel   with   concentrated 
sulphuric  acid ;   d,  calcium  chloride  tube ;   e,  bulb-tube  for  the 

1  Sieherheitsvorrichtnng  fur  Wasserstoffentwicklungsapparate  in  Fresenius's 
Zeitschr.  xvi.  93.     Poggendorf 's  Ann.  1876,  Heft  10. 


118  ASSAYING. 

reception  of  the  substance.  It  is  advisable  to  pass  the  gas  first 
through  a  solution  of  potassium  permanganate,  and  next  a  solu- 
tion of  sodium  hydrate  to  free  the  hydrogen  from  hydrocarbons, 
etc. 

4.  Assay  with  sulphocyanide.1 —  This  method  allows  of  the 
presence  of  nickle,  zinc,  iron,  and  arsenic;  0.5  to  1  gramme,  or 
more,  of  the  assay  sample  is  dissolved  in  nitric  acid  and  evapo- 
rated to  dryness  with  sulphuric  acid  until  the  free  sulphuric  acid 
is  completely  expelled. 

.  The  dry  mass  is  now  dissolved  with  a  little  water  and  a  large 
quantity  of  sulphuric  acid  added  to  the  cold  solution.  Potassium 
sulphocyanide  is  then  generally  added  until  white  copper  sub- 
sulphocyanide  is  precipitated  (if  too  much  potassium  sulphocyanide 
is  added  at  one  time,  the  black  sulphocyanide  is  formed  which  is 
only  gradually  reduced  to  sub-sulphocyanide  by  sulphurous  acid). 
A  sufficient  quantity  of  the  sulphocyanide  salt  has  been  added 
when  the  fluid  commences  to  assume  a  reddish-brown  color. 
This  coloration  is  caused  by  the  presence  of  iron,  but  the  fluid 
will,  in  a  short  time,  become  entirely  colorless.  The  precipitate 
is  allowed  to  settle  and  is  then  decanted  with  cold  water  until  a 
solution  of  silver  nitrate  is  not  rendered  turbid  by  the  wash  water. 
It  is  then  filtered  upon  a  previously  weighed  filter  and  dried  for 
12  hours  at  105°  to  110°  C.  (221°  to  230°  F.),  and  weighed 
(100  Cu2S2Cy2=52.2  Cu).  In  order  to  control  the  correctness  of 
the  result,  the  filter  is  incinerated  by  itself,  the  copper  sulphocya- 
nide is  heated  in  a  porcelain  crucible  to  decompose  the  sulphocya- 
nide, and  is  then  ignited  with  sulphur  in  a  current  of  hydrogen, 
and  treated  as  on  page  116. 

Nickel  coins. — 1  gramme  is  dissolved  in  10  cubic  centimeters 
of  nitric  acid  of  1.18  specific  gravity,  and  evaporated  to  dryness 
with  1  cubic  centimeter  of  concentrated  sulphuric  acid.  The  dry 
mass  is  dissolved  in  a  little  water,  and  to  the  solution  are  added 
50  cubic  centimeters  sulphurous  acid  solution,  and  2  grammes  of 
potassium  sulphocyanide.  After  having  stood  for  12  hours  it  is 
filtered,  etc.  For  the  determination  of  nickel  in  the  filtrate  see 
"  NICKEL." 

1  Fresenius's  Ztschr.  xvii.  55.  * 


COPPEE — WET   ASSAYS.  119 

Copper  alloyed  with  tin  (bronze). — 1  gramme  of  the  alloy  is 
dissolved  in  a  mixture  of  6  cubic  centimeters  of  concentrated 
nitrid  acid  of  1.5  specific  gravity  with  the  addition  of  3  cubic 
centimeters  of  water.  When  the  action  of  the  acid  has  ceased  the 
contents  of  the  dish  is  heated  for  a  time,  and  next  treated  with 
40  cubic  centimeters  of  boiling  water.  It  is  then  allowed  to  set- 
tle. The  sediment,  consisting  of  stannic  oxide,  containing  78.7 
per  cent,  of  tin  (free  from  copper)  is  washed  and  weighed.  If 
other  proportions  of  acid  are  used  the  stannic  oxide  will  be  cupri- 
ferous. If  black  specks,  which  will  indicate  nickel  sulphide, 
show  themselves  upon  solution,  some  hydrochloric  should  be 
added  to  the  nitric  acid.  Arsenic,  when  copper  is  precipitated 
with  potassium  sulphocyanide,  remains  in  the  filtrate.  Some  sul- 
phurous acid  is  added,  then  boiled  away,  and  the  arsenic  precipi- 
tated with  sulphuretted  hydrogen.  Iron  remains  with  the  nickel, 
and  may  be  separated  by  twice  dissolving  and  precipitating  with 
ammonia.  Sulphur  is  determined  by  barium  chloride. 

B.  Volumetric  assays.1 — A  large  number  of  precipitating 
methods  have  been  recommended;  according  to  Pelouze,  with 
sodium  sulphide ;  according  to  Galetti,  by  means  of  potassium 
ferrocyanide ;  according  to  Schwarz,  with  potassium  xanthate ; 
and,  according  to  Vollhard,  with  potassium  sulphocyanide.  Of 
reducing  methods,  the  following  are  recommended,  viz :  accord- 
ing to  de  Haen,  with  sodium  hyposulphite  and  potassium  iodide ; 
according  to  Weil,  with  protochloride  of  tin  ;  according  to  Parkes, 
with  potassium  cyanide ;  according  to  Schwarz,  with  ferric 
chloride  and  potassium  permanganate,  and  others.  The  method 
with  potassium  cyanide  is  largely  used  in  smelting  works,  for  the 
reason  that  it  is  easily  executed,  and  affords  a  sharp  final  reaction. 
Weil's  method  with  protochloride  of  tin  is  also  simple,  and  both 
methods  are  particularly  well  adapted  for  the  further  test  of  the 
impure,  black,  precipitated  copper  obtained  in  the  Swedish  assay 
(pp.  107,  108). 

1  Mohr,  Lehrb.  der  Titrirmethode,  1874,  pp.  214,  262,  319,  473,  665  ;  B.  u. 
h.  Ztg.  1871,  p.  222  (Pelouze)  ;  1869,  p.  19  ;  1877,  p.  207  (Schwarz)  ;  1870, 
p.  447  ;  1872,  p.  26  ;  Oestr.  Zeitschr.  1871,  No.  xvii.  ;  Oestr.  Jahrb.  der  Ber- 
gakademien  u.  s.  w.  Bd.  xx.  p.  133  (Weil)  ;  Fresenius's  Ztschr.  xvii.  53 
(RhodTanprobe). 


120  ASSAYING. 

1.  Parkes's  assay  with  potassium  cyanide.1 — This  method  is 
based  upon  the  reduction  of  an  ammohiacal  solution  of  copper 
by  treatment  with  potassium  cyanide.  The  blue  color  of  the 
solution  disappears  and  colorless  cyanide  of  copper  and  ammo- 
nium is  formed  (4CuN,O6+  8KCy+2Am2O=4  CuCy-f  2AmCy 
+  8KNO3  +  2Am,CyO).  Foreign  metals  which  give  a  solution 
of  peculiar  color  with  ammonia  (nickel,  cobalt)  or  which  form  a 
colorous  solution  (zinc,  manganese)  exert  a  disturbing  effect,  as  do 
also  such  as  produce  a  precipitate  which  it  is  difficult  to  free  from 
hydrated  oxide  of  copper  in  washing  (ferric  oxide,  alumina)? 
Lead,  silver,  tin,  and  antimony  may  be  removed  in  advance.  The 
presence  of  arsenic*  is  harmless,  provided  no  ferric  oxide  is 
present  at  the  same  time,  since  ferric  arsenate  is  soluble  in  am- 
monia. This  method  is  much  used  in  practice,  and  gives  suffi- 
ciently accurate  results,  provided  the  same  conditions  are  always 
observed  (i.  e.,  uniform  dilution,  the  use  of  the  same  quantities 
of  acids  and  ammonia,  etc.). 

The  following  quantities  of  ore  are  dissolved  : — 

10    grammes  of  ore,  when  it  contains  0.1  to    1  per  cent.  Cu. 
5  "          "  "  "          1     to    5        "  " 

2.5          "          "  "  "  5      to  30       "  " 

Ito0.5  "         "  "  "        30     to  80       "  " 

The  assay  sample  is  dissolved  in  nitric  acid,  and,  if  it  contains 
lead,  is  evaporated  nearly  to  dryness  with  sulphuric  acid.  It  is 
then  diluted  with  water  to  the  bulk  of  J  liter  and  (if  the  above- 
mentioned  injurious  foreign  metals  are  present)  precipitated  from 

i  B.  u.  h.  Ztg.  1867,  p.  102  ;  1869,  p.  18 ;  1871,  p.  222;  1872,  pp.  207,  347, 
419.  Oestr.  Jahrb.  xx.  133. 

[2  According  to  Messrs.  Torrey  and  Eaton  of  New  York,  Engineering  and 
Mining  Journal,  vol.  39,  pp.  317,  386,  441.  Three  per  cent,  of  zinc  causes  an 
apparent  increase  of  £  per  cent,  copper.  From  5  to  15  per  cent,  arsenic  does 
no  harm,  25  per  cent,  silver  caused  an  error  of  y1^  per  cent,  copper,  30  per 
cent,  iron  caused  a  loss  of  3.71  per  cent,  copper.  From  5  to  40  per  cent,  lead 
had  no  injurious  effect.  20  per  cent,  bismuth  made  the  same  error  as  silver. 

-a.] 

[3  It  seems  doubtful  if  the  presence  of  arsenic  is  harmless,  as  sometimes 
when  it  is  present  the  end  of  the  titration  is  obscured  by  a  yellowish  green 
tint  which  replaces  the  blue  color  of  the  ainmoniacal  solution.  Trans.  Am. 
Inst.  M.  E.,  vol.  9,  p.  316.— G.] 


COPPER — WET  ASSAYS.  121 

the  acid  solution  with  sulphuretted  hydrogen.  The  precipitate  of 
copper  sulphide  is  filtered,  and  washed  on  the  filter  with  a  solu- 
tion of  sulphuretted  hydrogen.  It  is  then  rinsed  off  from  the 
filter  into  the  same  flask,  which  was  used  for  the  solution,  and  is 
heated  with  10  cubic  centimeters  of  concentrated  nitric  acid  of 
1.41  specific  gravity  until  the  sulphur  is  seen  to  separate  in  the 
form  of  globules.  Ammonia  is  now  added  until  precipitation 
takes  place,  then  20  cubic  centimeters  of  ammonium  carbonate 
solution  (1  : 10)  are  added.  The  quite  clear  solution  is  filtered  off 
from  the  sulphur  into  a  beaker  glass.  The  sulphur  remaining  in 
the  flask  is  treated  with  hydrochloric  acid  and  potassium  chlo- 
rate until  it  is  entirely  dissolved.  It  is  then  evaporated  to  dry- 
ness  on  the  sand-bath,  and  the  residue  is  treated  as  above  with 
water,  ammonia,  and  carbonate  of  ammonium,  and  filtered  into 
the  principal  solution.  The  filter,  from  which  the  precipitate  of 
copper  sulphide  was  washed  off,  is  spread  out  in  a  beaker  glass. 
Water  is  poured  over  it,  a  few  drops  of  nitric  acid  are  added  to 
it,  and  it  is  then  boiled  for  a  few  minutes.  Ammonia  and  car- 
bonate of  ammonia  are  added  as  above,  and  the  solution  is  like- 
wise filtered  into  the  original  solution,  which  is  then  diluted  to 
the  bulk  of  J  liter  and  should  have  only  a  faint  odor  of  ammonia. 
20  cubic  centimeters  of  the  liquid  are  taken  and  titrated  with  a 
solution  of  potassium  cyanide  until  the  color  has  so  nearly  disap- 
peared that  only  a  faint  violet  tint  remains  (best  seen  in  a  porce- 
lain dish)  and  which  entirely  disappears  in  from  1  to  2  minutes 
(by  titrating  at  60°  C.  (140°  F.)  the  percentage  of  copper  found 
will  be  somewhat  less,  but  more  accurate). 

The  potassium  cyanide  is  standardized  as  follows,  and  should 
be  used  in  as  fresh  a  condition  as  possible,  viz :  5  grammes  of 
potassium  cyanide  are  dissolved  in  J  liter  of  water,  and  1  gramme 
of  electrolytic  copper  in  nitric  acid.1 

The  solution  is  supersaturated  with  ammonia  and  ammonium 
carbonate,  and  diluted  as  above  to  the  bulk  of  1  liter.  100  cubic 
centimeters  of  the  solution  will  then  contain  0.1  gramme  of  cop- 
per from  which  the  potassium  cyanide  may  be  standardized. 

1  [This  copper  should  invariably  be  tested  for  its  purity. — G.] 


122  ASSAYING. 

In  titrating  an  ammoniacal  solution  of  copper  with  potassium 
cyanide  the  presence  of  4.5  per  cent,  of  zinc  does  not,  according  to 
Peters,1  exert  an  injurious  effect  upon  the  results  of  the  assay.  In 
a  quartz  of  copper  ore  containing  only  copper,  zinc,  and  iron,  the 
presence  of  5  per  cent,  zinc  causes  a  constant  error  of  0.22  per  cent., 
which  increases  with  the  amount  of  zinc.  The  presence  of  arsenic 
and  antimony  up  to  one  per  cent,  causes  an  error  of  0.5  per  cent, 
and  if  over  one  per  cent,  of  these  metals  be  present  the  assay  be- 
comes useless. 

Steinbeck's  modified  method  of  assaying  copper? — In  the  copper 
works  of  the  Ducktown  district  in  Tennessee,  2  grammes  of  ore  are 
digested  with  HOI  until  the  evolution  of  gas  has  ceased ;  5  c.c.  of 
strong  HN03  are  then  added,  and  after  evaporation  with  H3S04  to 
dryness,  the  residue  is  taken  up  with  water  containing  H2S04  and 
filtered  into  a  beaker  containing  metallic  zinc  and  some  water. 
What  remains  undissolved  is  then  washed  upon  the  filter  with  hot 
water,  the  zinc  is  lifted  from  the  copper  with  a  pair  of  forceps,  and 
the  copper  filtered  off.  The  latter  is  then  dissolved  in  a  few  drops 
of  HN03,  the  solution  made  ammoniacal,  and  titrated  with  potas- 
sium cyanide.  In  the  solution  freed  from  copper  the  iron  is  titrated 
with  potassium  bichromate  and  the  residue  remaining  undissolved, 
weighed.  These  three  determinations  generally  suffice  for  working 
assays. 

Copper  precipitated  with  iron  (p.  106),  or  with  zinc  (p.  108). 
Mansfeld  copper  schist  (Kupferschiefer)  may  be  examined  by 
this  method  by  dissolving  5  grammes  of  the  precipitated  copper 
(pp.  109, 110)  in  from  8  to  16  cubic  centimeters  of  nitric  acid 
of  1.2  specific  gravity.  The  solution  is  gently  heated,  allowed 
to  cool,  and  is  then  supersaturated  with  10  cubic  centimeters  of 
a  mixture  of  1  volume  ammonia  and  2  volumes  of  water.  It  is 
titrated  with  potassium  cyanide,  1  cubic  centimeter  of  which 
represents  0.005  gramme  of  copper.  It  is  advisable  to  preserve 
the  solution  of  potassium  cyanide  in  the  dark,  in  a  tightly  stop- 
pered flask  of  green  glass. 

2.  Fleitmann's  method  with  ferric  chloride.9 —  Copper  precipi- 

*  Engineering  and  Mining  Journal,  1885,  vol.  39. 

2  Bu.  u.  Hltumsch,  Ztg.  1886,  p.  454. 

3  Ann.  d.  Cuem.  u.  Pharm.  xcviii.  141. 


OF  a 

™\^r 

_  ---  -~-±^^ 

COPPER — WET   ASSAYS.  123 

tated  by  zinc,  as  described  on  p.  108,  is  dissolved  in  a  mixture 
of  ferric  chloride  and  hydrochloric  acid.  The  solution  should  be 
made  in  a  glass  flask  furnished  with  a  rubber  valve  (Fig.  11,  p. 
36),  and  with  the  addition  of  a  little  sodium  carbonate  to  expel 
the  air.  Protochloride  of  iron  (Cu  +  Fe2Clfi  «  CuCl2  +  2FeCl2) 
is  formed,  which  is  titrated  with  potassium  permanganate  until  a 
pinkish  coloration  remains  permanently. 

The  standard  of  the  solution  of  potassium  permanganate  is 
fixed  as  follows :  0.2  to  0.3  gramme  of  piano  wire,  containing 
at  an  average  0.4  per  cent,  carbon,  is  placed  in  a  flask  provided 
with  a  mark  at  200  cubic  centimeters  and  dissolved  in  diluted 
sulphuric  acid,  the  air  being  excluded.  It  is  allowed  to  cool  off, 
and  is  then  diluted  to  200  cubic  centimeters  with  distilled  water 
previously  boiled.  Solution  of  potassium  permanganate  (pre- 
pared as  below)  is  then  added,  drop  by  drop,  to  100  cubic  centi- 
meters of  the  solution  of  iron  until  the  light  rose-red  coloration 
remains  permanently.  This  operation  is  repeated  with  the  re- 
maining 100  cubic  centimeters  of  iron  solution.  From  these 
titrations  the  value  of  the  permanganate  may  be  calculated. 
The  flask,  during  the  operation,  should  be  placed  upon  white 
paper,  as  this  will  aid  in  accurately  recognizing  the  tint  of  the 
solution  which  indicates  the  end  of  the  reaction.  The  solution 
of  potassium  permanganate  is  made  by  dissolving  4.5  grammes 
of  potassium  permanganate  in  1  liter  of  water,  when  1  cubic 
centimeter  of  the  solution  will  correspond  to  0.008  gramme  of 
iron.  It  is  advisable  to  have  1  cubic  centimeter  of  the  perman- 
ganate solution  correspond  to  from  6  to  10  milligrammes  of  iron, 
as  with  this  strength  one  drop  of  the  solution  will  produce  a  per- 
ceptible tint.  1  equivalent  Cu  (31.50)  —  2  equ.  Fe  (55.90).  In- 
stead of  using  dissolved  iron,  the  strength  of  the  permanganate 
solution  may  be  determined  with  the  double  sulphate  of  iron  and 
ammonia,  containing  6  eq.  H2O,  and  representing  14.286  per 
cent,  of  metallic  iron. 

If  the  original  solution  of  copper  contains  nitric  acid,  bismuth, 
or  lead,  it  is  precipitated  with  ammonia  in  excess  and  filtered. 
The  copper  is  then  precipitated  with  the  aid  of  heat,  by  means  of 
finely  divided  zinc,  in  arnrnoniacal  solution. 


124  ASSAYING. 

3.  Method  with  sodium  sulphide  in  an  ammoniacal  solution.1 — 
The  solution  must  be  heated  to  60°  to  80°  C. — between  these  tem- 
peratures an  oxysulphide  is  precipitated,  while  at  ordinary  tempera- 
tures CuS  falls,  which,  does  not  readily  subside.    If  the  precipitation 
is  conducted  at  a  higher  temperature,  another  oxysulphide  contain- 
ing more  oxygen  is  precipitated,  and  copper  may  remain  in  solution 
without  coloring  the  fluid.     The  solution  is  placed  over  a  lamp  in 
a  flask,  and  a  thermometer  inserted  in  the  liquid ;  when  the  tem- 
perature reaches  75°  C.  the  lamp  is  withdrawn  and  sodium  sulphide 
added  from  a  burette  until  the  blue  color  has  completely  disappeared. 
In  an  acid  solution. — The  solution  is  diluted  with  hot  water  to 
about  200  c.c.  in  a  stoppered  flask,  acidified  with  HC1,  and   the 
sodium  sulphide  run  in,  replacing  the  stopper  and  shaking  after  each 
addition.      The  copper   sulphide  produced  separates  rapidly,  and 
leaves  a  clear  solution  above  it.     The  sodium  sulphide  is  added 
until  no  further  precipitate  is  produced. 

Sodium  sulphide  decomposes  slowly,  and  its  strength  is  deter- 
mined by  means  of  a  solution  of  copper  sulphate  containing  39.356 
grammes.  CuS04  +  5H20  per  liter.  The  determination  of  the 
strength  of  the  sodium  sulphide  must  be  made  as  it  is  to  be  used  ;  if 
the  copper  is  to  be  determined  in  acid  solution,  the  copper  sulphate 
taken  for  determination  must  be  acidified.  If,  on  the  contrary,  the 
estimation  is  to  be  made  in  an  ammoniacal  solution,  the  copper 
taken  is  made  strongly  ammoniacal. 

For  the  better  recognition  of  the  final  reaction  in  the  determina- 
tion of  copper  with  sodium  sulphide,  P.  Casamajor2  recommends 
the  precipitation  of  the  copper  from  an  alkaline  solution  containing 
tartaric  acid.  Dissolve  173  grammes  of  Rochelle  salt  (sodium  tar- 
trate)  in  water,  add  480  c.c.  of  caustic  soda  of  specific  gravity  1.14, 
dilute  the  mixture  to  form  1  liter  of  solution,  and  add  a  slight  excess 
of  the  copper  solution  to  it.  The  deep  blue  liquid  is  then  heated  in 
a  porcelain  dish  to  boiling,  and  titrated  with  sodium  sulphide. 

4.  Method  with  protochloride  of  tin. — Weil  has  perfected  this 
method  by  first  removing  after  the  solution  of  the  ore  in  HN03,  or 
HC1  -f  HNO3,  the  greater  part  of  the  acid  from  the  solution  by 
evaporating  nearly  to  dryness,  diluting  to  250  c.c.      From  10  to  25 
c.c.  of  the  diluted  solution  are  taken  out,  and  after  adding  an  excess 
of  HC1,  again  evaporated  until  the  vapors  no  longer  give  a  blue 

1  Volumetric  Analysis,  Hart.     New  York,  1878,  pp.  152-153. 

2  Chem.  News,  vol.  45,  p.  147.     1882. 


COPPER — WET  ASSAYS.  125 

color  to  paper  saturated  with  potassium  iodide  The  solution  is 
finally  mixed  with  an  equal  volume  of  pure  HC1  and  titrated.  The 
color  reaction  is  extremely  sharp  and  every  possible  loss  from  sput- 
tering avoided  by  evaporation  with  H2S04. 

5.  Fresenius  recommends  the  following  method  of  Haerfs.1 — 
Dissolve  the  compound  of  copper  in  H2S04,  reduce  to  a  neutral 
solution.  Dilute  solution,  in  a  measuring  flask,  to  a  definite 
volume ;  100  c.c.  should  contain  from  1  to  2  grms.  of  Cu.  Intro- 
duce about  10  c.c  of  KI  solution  (1  to  10)  into  a  stoppered  bottle, 
add  10  c.c.  of  the  Cu  solution,  mix,  allow  to  stand  10  minutes,  and 
then  determine  the  separated  iodine,  either  with  sulphurous  acid  and 
iodine,  or  with  sodium  thiosulphate.  The  Cu  solution  must  be  free 
from  ferric  salts  and  other  bodies  which  decompose  KI,  also  free 
HN03,  and  free  HC1;  and  the  solution  must  not  be  allowed  to 
stand  too  long  before  titration.  With  strict  attention  to  these  rules 
the  results  are  accurate. 

C.  Colorimetrie  methods.2 

1.  Heine's  assay  for  poor  ores  and  products  (slags,  etc.).  Stand- 
ard solutions,  containing,  respectively,  0.025,  0.02,  0.015,  0.01, 
and  0.005  gramme  to  every  120  cubic  centimeters  of  liquid,  are 
prepared  either  by  dissolving  a  known  weight  of  copper  and  di- 
luting this  as  much  as  may  be  necessary  to  obtain  the  separate 
gradations  of  copper,  mentioned  above,  in  equal  volumes  of  the 
liquid  ;  or  by  directly  weighing  off  the  above-mentioned  quan- 
tities of  electrolytic  copper  and  dissolving  each  with  a  few  drops 
of  nitric  acid  in  a  graduated  vessel,  adding  ammonia  in  excess  and 
diluting  the  clear,  blue  fluid  with  distilled  water  to  120  cubic 
centimeters.  The  solutions  are  then  introduced  into  oblong 
sample-glasses,  having  exactly  the  same  form  and  sectional  area, 
about  50  millimeters  long,  50  millimeters  wide,  and  110  milli- 
meters high.  They  should  be  closed  with  ground-glass  stoppers, 
and  marked  on  the  outside  with  figures,  representing  the  strength 
of  the  solutions  ;  in  this  case,  0.025,  0.02,  0.015,  0.01,  and  0.005 
gramme  Cu  in  120  cubic  centimeters.  The  solution  to  be  tested 
is  prepared  in  the  following  manner :  5  grammes,  or  more,  of  ore 

1  Quantitative  Chemical  Analysis,  1881,  p.  317. 

2  Dingier,  1857,  p.  436.     Berggeist,  1867,  No.  27.     Percy's  Metallurgy  of 
Copper,  Zinc,  and  Brass,  pp.  487,  488. 


126  ASSAYING. 

are  dissolved,  from  which  an  ammbniacal  copper  solution  is  pre- 
pared in  the  same  manner  as  in  the  assay  with  potassium  cyanide 
(p.  120).  The  volume  of  the  solution  is  measured  to  cubic  centi- 
meters, and  it  is  then  poured  into  an  empty  standard-glass.  The 
intensity  of  the  color  of  the  solution  is  compared  with  that  of  the 
standard  solutions,  the  glasses  being  held  against  a  sheet  of  white 
paper,  and  it  is  observed  with  which  of  them  it  corresponds  in 
intensity  of  color.  The  percentage  of  copper  is  then  calculated, 
due  consideration  being  given  to  its  volume. 

Suppose  5  grammes  of  ore  had  been  used,  and  300  cubic  centi- 
meters of  solution  had  been  obtained,  the  color  of  which  corre- 
sponded to  the  standard  liquid  containing  0.02  gramme  in  120 
cubic  centimeters ;  the  copper  in  5  grammes  would  then  amount 
to  1  per  cent.  (120  : 0.02  =  300  :x). 

If  the  assay  solution  is  darker  than  the  darkest  standard  solu- 
tion, it  is  diluted  to  a  known  volume  with  water,  until  it  corre- 
sponds with  one  of  the  standards.  Should  the  reverse  be  the 
case,  the  solution  under  examination  is  evaporated  to  a  known 
volume.  This  method  is  less  accurate  where  high  percentages 
are  involved,  as  errors  in  observation  will  be  multiplied.  It  is 
best  to  determine  in  this  way  from  1  to  2  per  cent,  of  copper  at 
the  utmost. 

In  precipitating  copper  solutions  containing  iron,  by  means  of 
ammonia,  the  ferric  hydrate1  always  retains  some  copper.  This 
error  is  equalized  by  adding,  in  preparing  the  standard  solutions, 
a  quantity  of  iron  corresponding  about  to  the  percentage  of  iron 
in  the  assay  sample  (assay  of  slag  in  Swansea.)  Organic  sub- 
stances, in  presence  of  nitric  acid,  produce  with  ammonia  a 
greenish  tint,  which  exerts  a  disturbing  effect  in  comparing  the 
color  of  the  copper  solution  (therefore,  copper-schist  should  be 
ignited  and  niters  incinerated  before  they  are  brought  in  contact 
with  nitric  acid).  Ammoniacal  solutions  which  may  become  tur- 
bid (for  instance,  if  diluted  with  ordinary  water  containing  lead) 
are  allowed  to  become  clear,  and  are  filtered  once  more. 

2.  Jaquelin-Hubert's  method  for  considerable  percentages  of  cop- 
per.— Only  one  normal  or  standard  solution  of  known  strength 

i  B.  u.  h.  Ztg.  1869,  p.  302. 


COPPER — WET   ASSAYS.  127 

is  used.  This  is  compared  with  the  solution  under  examination 
in  a  graduated  glass  tube  (calibrated).  If  richer  than  the  stand- 
ard, the  assay  solution  is  diluted  to  correspond  with  the  former ; 
and  if  poorer,  the  standard  solution  is  correspondingly  diluted, 
until  an  equal  intensity  of  color  has  been  obtained.  From  the 
relative  volumes  the  percentage  of  copper  is  then  readily  calcu- 
lated. The  solution  contains  0.5  gramme  of  copper  in  1000  cubic 
centimeters.  As  errors  of  observation  may  easily  occur,  a  gravi- 
metric or  volumetric  assay  is  frequently  preferred  for  larger 
percentages  of  copper. 

Determination  of  arsenic  in  copper. — According  to  Pattinson,1 
the  process  is  as  follows :  The  copper  is  dissolved  in  HNO3,  and 
sufficient  caustic  soda  added  to  a  little  more  than  neutralize  the  free 
acid  present,  the  arsenic  is  precipitated  as  copper  arsenate.  This 
washed  precipitate  is  dissolved  in  HN03,  a  slight  excess  of  ammonia 
added,  and  the  arsenic  is  determined  by  magnesia  mixture. 

Sexton  prefers  to  precipitate  the  arsenic  from  the  nitric  acid  solu- 
tion (by  adding  sodium  acetate  and  boiling)  as  basic  acetate.  The 
precipitate  is  dissolved  in  acid,  reprecipitated  by  H2S,  oxidized  to 
arsenic  acid,  and  determined  as  the  magnesia  compound. 

Determination  of  phosphorus  in  copper? — If  phosphorus  is  also 
to  be  determined  in  the  copper,  the  magnesium  salt  is  redissolved 
in  HC1,  the  arsenic  precipitated  by  H2S,  and  the  phosphoric  acid  in 
the  filtrate  again  determined  as  ammonium-magnesium  salt,  whose 
weight  deducted  from  that  previously  found  gives  as  a  balance  the 
pure  arsenate  of  magnesium. 

Rynoso  determines  the  phosphorus  in  phosphor  copper  by  adding 
to  the  weighed  sample  at  least  ten  times  its  weight  of  tin  (i.  e.,  such 
a  quantity  as  to  more  than  equal  the  amount  of  phosphorus  supposed 
to  be  present  and  converted  by  oxidation  into  phosphoric  acid)  and 
boiling  with  an  excess  of  concentrated  HN03  for  about  three  hours. 
The  tin  in  oxidizing  absorbs  all  the  phosphoric  acid  and  when  decom- 
position is  complete,  filter,  and  heat  the  phosphate  of  tin  to  prevent 
reduction  by  any  carbonaceous  material  present.  The  ash  of  the 
filter  is  always  black  and  must  be  completely  incinerated  by  moisten- 
ing it  with  HNO3,  and  igniting.  It  is  also  advisable  to  treat  in  the 

1  Newcastle-on-Tyne  Chem.  Soc.  Feb.  1882.      Polytechnisches  Notizblatt, 
1882,  p.  237. 

2  Fortscliitte  im  Probirwesen.     Balling.     Berlin,  1887,  p.  96. 


128  ASSAYING. 

same  manner  the  phosphate  of  tin.  From  the  weight  of  the  ignited 
phosphate  of  tin  deduct  the  weight  of  the  oxide  of  tin  calculated 
from  the  weight  of  metallic  tin  used  in  the  experiment.  The  re- 
mainder is  phosphoric  acid  formed  by  oxidation  of  the  phosphorus, 
from  which  the  content  of  phosphorus  is  formed  by  multiplying  by 
0.436. 

The  method  is  readily  performed,  but  requires  the  use  of  perfectly 
pure  tin,  as  the  slightest  impurities  give  rise  to  serious  errors. 

A  modification  of  this  process  by  Reisig  is  found  in  H.  Kgse's 
"Handbuch  der  Analytischen  Chemie,"  6  Ausflage,  p.  520. 

Ill,  SILVER, 

30.    PRINCIPAL   ORES. 

Native  silver;  amalgam,  Ag  and  Hg,  with  26.5  to  86  Ag; 
antimonial  silver  Ag  and  Sb,  with  59  to  84  Ag ;  silver  telluride 
(hessite),  Ag2Te,  with  62.79  Ag ;  silver  glance,  Ag2S,  with  87.1 
Ag ;  brittle  silver  ore  (stephanite),  Ag5SbS4,  with  68.56  Ag ;  ruby 
silver  (pyrargyrite),  Ag3(Sb,As)S3,  with  65.38  to  59.98  Ag ;  miar- 
gyrite,  AgSbS2,  with  35.86  Ag;  polybaxite,  Ag(Cu,Fe,Zn)9Sb 
(As)S6,  with  64  to  75  Ag ;  stromeyerite,  CuAgS,  with  53  Ag ; 
horn  silver,  AgCl,  with  75.26  Ag ;  iodyrtte  (silver  iodide)  Agl, 
with  46  Ag ;  bromyrite  (silver  bromide)  AgBr,  with  57.45  Ag. 

31.   ASSAYS  FOR  NON-ALLOYS.1 

The  fire-assay  methods  are  based  upon  the  principle  of  decom- 
posing the  silver  ore  by  means  of  lead  or  lead  oxide,  collecting 
the  silver  thus  set  free  with  an  excess  of  the  lead,  the  slagging  off 
of  foreign  substances  by  suitable  fluxes,  and  the  cupellation  of 
the  lead  button  to  separate  the  silver.  The  collection  of  silver  in 
a  lead  button  is  effected,  according  to  the  nature  of  the  foreign 
admixtures,  either  in  a  scorifier  (scorincation  assay)  or  in  a  cruci- 
ble (crucible  assay). 

1  Blossom,  flold  and  Silver  Assays,  in  Am.  Chemist,  Jan.  1871,  p.  250  ; 
Aaron,  Pract.  Treatise  on  Testing  and  Working  Silver  Ores,  San  Francisco, 
1877.  Percy's  Metallurgy  of  Silver  and  Gold,  vol.  1.  John  Murray,  London, 
1880,  pp.  224-301. 


SILVER — ASSAYS  FOR  NON-ALLOYS.  129 

The  crucible  assay  permits  of  a  large  quantity  of  assay  sample 
being  used  (which  reduces  the  error  from  a  loss  of  silver),  and  for 
this  reason,  it  may  be  especially  recommended  for  poor  ores  and 
such  compounds  as  are  free  from  antimony  and  arsenic  (chloride, 
bromide,  and  iodide  of  silver  and  slags),  and  also  for  ores  or 
sweepings  of  a  very  complex  composition.  The  scarification  as- 
say is  better  adapted  for  ores  containing  sulphur,  antimony,  and 
arsenic,  though  likewise  for  other  ores,  so  that  this  may  be  called 
an  assay  of  general  applicability ;  but,  nevertheless,  for  the  first- 
named  ores,  etc.,  the  crucible  assay  is  simpler  and  cheaper  and 
the  result  is  more  quickly  attained.  In  America  the  crucible  assay 
is  chiefly  used,  while  the  scarification  assay  is  preferred  in  Ger- 
many, although  neither  possesses  any  material  advantage  over 
the  other.1 

Wet  assays  are  less  commonly  used. 

I.  Fire  Assays. 

A.   Collecting  the  silver  with  lead. 

1.  Scarification  assay. — This  consists  of  an  oxidizing  fusion  of 
the  ores  with  lead,  which  becomes  oxidized  and  yields  up  oxygen 
to  the  metallic  sulphides,  arsenides,  and  antinionides,  forms  a 
slag  with  the  oxides  thus  formed  and  with  the  earths  which  may 
be  present.  The  slagging  off  of  basic  earths  is  promoted  by  an 
addition  of  borax  glass.  The  following  points  must  be  taken 
into  consideration  in  preparing  the  charge. 

a.  The  quantity  of  lead  to  be  used  will  depend  on  whether  the 
metallic  sulphides,  arsenides,  and  antinionides  are  easily  or  with 
difficulty  decomposed  by  lead  oxide  (p.  7 6),. or  whether  they  are 
entirely  absent.  Either  granulated  lead  free  from  silver,  which 
is  measured  (p.  29),  is  used,  or  argentiferous  lead,  whose  percent- 
age of  silver  is  deducted  from  the  assay  by  placing  the  silver 
button  obtained  from  a  corresponding  quantity  in  the  balance 
pan  with  the  weights  in  weighing. 

i  B.  u.  h.  Ztg.  1867,  p.  102  ;  1874,  p.  68  ;  1877,  p.  232. 
[The  scorification  assay  is  generally  preferred  for  rich  ores,  while  the  cru- 
cible assay  is  perhaps  better  adapted  to  the  poorer  ones. — Gr.] 
9 


130  ASSAYING. 

Lead  sulphide  is  the  easiest  to  decompose,  next  the  sulphides  of 
iron  and  zinc,  and  then  eopper  sulphide.  The  most  difficult  are 
the  sulphurized  and  arsenized  nickel  and  cobalt  ores. 

b.  The  quantity  of-  borax  depends  on  the  degree  of  infusibility 
of  the  gangue  (silicic  acid  and  aluminous  substances  require  but 
little,  and  lime  and  magnesia,  much  borax)  and  of  the  metallic 
oxides  which  are  formed  (ferric  oxide,  zinc  oxide,  stannic  oxide, 
and  nickel  and  cobalt  ores  require  much,  oxides  of  copper,  bis- 
muth, etc.,  but  little). 

In  all  cases,  but  little  borax  should  be  taken  at  first,  to  prevent 
the  entire  surface  of  the  charge  from  being  covered,  as  this  would 
exclude  the  air.  If  more  borax  is  necessary,  it  is  added  before 
the  final  heating.  Much  antimony  and  zinc  oxide  cause  the 
cupels  to  become  full  of  cracks. 

c.  The  number  of  samples  to  be  taken  to  control  the  accuracy 
of  results  will  vary  according  to  the  richness  of  the  ores,  their 
want  of  uniformity,  etc.,  from  2  to  10  or  more. 

d.  If  the  ore  contains  less  than  1  per  cent,  of  silver,  5  grammes 
or  about  $•  A.  T.1  are  taken  for  a  charge,  if  more  than  1  per  cent., 
2.5  grammes  (from  ^  to  ^  A.  T.),  and  of  very  rich  ores,  .1  to 
0.5  gramme  or  about  fa  to  -fa  A.  T.     In  assaying  very  poor 
ores,  the  lead  buttons  obtained  by  scorification  are  concentrated 
by  further  scorification. 

The  following  table  gives  some  examples  of  various  charges: — 

1  Assay  ton  =  29.166  grammes. 


SILVER — ASSAYS   FOR   NON- ALLOYS. 


131 


Argentiferous  substances. 

Test  lead  : 
times  the 
quantity 
of- 
substance. 

Borax 
glass: 
per  cent. 

Remarks. 

Amalgamation  residues 

12  to  15 

to  15 

Two    assay   samples,   each    5 

grammes  (or  say  £  A.  T.)  are 

scorified,  and  the  two  buttons 

obtained  are  cupelled. 

Antimonial  ores    .     .     . 

16 

200 

Assay  sample  1.25  grammes, 

about  fa  A.  T. 

Antimonial  silver       .     . 

32 

300 

The  same. 

German-silver,  or  China 

20  to  24 

to  40 

2.5  grammes  (T^  to  ^  A.  T.). 

silver 

Arsenical  ores       .     .     . 

to  16 

to  50 

Require  a  high  temperature  in 

scorifying. 

Galena,  pure    .     .     .     . 

6 

Oto  15 

"       siliceous  .     .     . 
"       zinciferous    .     . 

|     toll 

20  to  30 

Lead  speiss       .... 

10  to  20 

15  to  25 

2.5  grammes  (T\j-  to  ^  A.  T.) 

are  used  for  the  charge.    The 

buttons-  obtained   from    two 

•  assays  are  again  fused,  with 

a  little  borax  at  first,  then 

with  addition  of  more. 

9  to  20 

12  to  25 

"     nickeliferous     .     . 

11  to  14 

20  to  24 

20  to  25 

2.5  grammes  (from  y1^-  to  TV  A. 

T.)  are  used  and  repeatedly 

scorified. 

Darrkupfer1      .... 

18  to  20 

10 

Charge  same  as  above. 

Milling  silver  ores  — 

common     .... 

12  to  15 

to  15 

basic     

8 

25  to  50 

acid       

8 

Oto  20 

siliceous     .... 

12  to  14 

10  to  15 

Iron,  cast-iron       .     .     . 

8  to  12 

2  to  3 

The  iron  .  is  first  oxidized   in 

1  glass 

the  muffle  by  admitting  air, 

or  by  means  of  nitric  acid. 

Fluthafter2       .... 

12  to  15 

15 

Several  assays,  as  many  as  30, 

are  made,  and  the  lead  but- 

tons   obtained   are    scorified 

into  one,  and  this  is  cupelled. 

Refined  copper      .     .     . 

18  to  20 

1  to  5 

Charge  2.5  grammes  (j1^  to  jV 

A.  T.). 

Sweepings,  argentiferous 

8  to  9 

Oto  20 

See  p.  20. 

and  auriferous 

Hearth  bottoms     .     .     . 

8 

10  to  20 

Gun-metal  

20  to  24 

20  to  25 

Charge  2.5  grammes  (T^  to  -j-1^ 

A.  T.). 

Kiehnstocke3    .... 

18  to  20 

10 

The  same. 

Cobaltiferous  ores      .     . 

20 

15  to  20 

Cupriferous  ores    .     .     . 

10  to  20 

10  to  15 

Copper  matt     .... 

12  to  15 

10  to  15 

C1  Copper  reduced  by  the  liquation  or  drying  process. — G.] 
[2  Ore  from  placer  deposits  (wash  ore). — G.] 
[8  Residual  copper  from  liquation  process. — G.] 


132 


ASSAYING. 


Argentiferous  substances. 

Test  lead: 
times  the 
quantity 
of 
substance. 

Borax 
glass: 
per  cent. 

Remarks. 

20  to  24 

15  to  20 

The  same. 

Nickeliferous  ores      .     . 

20 

15  to  20 

The  same. 

Furnace  deposits  .     .     . 

12  to  14 

10  to  15 

Raw  matt    

10  to  12 

to  30 

Only  a  small  quantity  of  borax 

at  first. 

Slags       

12  to  15 

10  to  15 

The  same  as  fluthafter. 

Black  copper    .... 

18  to  20 

10  to  15 

Charge  2.5  grammes  (T\-  to  TV 

Residue  from  the  amal- 

] 

[A.  T.). 

gamation  of  black  cop- 
per and  extraction  of 

j-  8  to  10 

1  to  10 

The  same. 

silver 

j 

Zinciferous  ores     .     .     . 

10  to  16 

15  to  25 

Fusion  at  a  high  temperature. 

Argentiferous  zinc     .     . 

16 

16 

Charge  1.25  grammes  (about 

* 

^  A.  T.)  of  zinc  oxide  with 

16  parts  of  lead  and  16  parts 

of  borax. 

Stanniferous  ores       .     . 

20  to  30 

15  to  25 

They  are  scorified  several  times 

Argentiferous  tin       .     . 

16 

16 

Charge  1.25   grammes  (about 

•^5  A.   T.)  of  stannic  oxide, 

with  16  parts  of  lead  and  4 

parts  borax  glass. 

The  quantity  of  test  lead  required  according  to  the  foregoing 
table  is  measured  or  weighed  off,  and  divided  approximately  into 
two  parts.  The  accurately  weighed  assay  sample  is  mixed  with 
one-half  of  the  lead  in  the  bottom  of  the  scorifier  and  the  mixture 
is  covered  over  with  the  remaining  part  of  the  lead,  and  finally 
the  borax  is  added.  The  charged  scorifier  is  placed  in  a  strongly 
heated  muffle,  the  mouth  of  which  is  closed,  and  a  strong  draft 
kept  up  for  the  purpose.  The  lead  will  soon  commence  to  fuse,  and 
in  sinking  down  absorb  silver  from  the  ore.  This,  on  rising  to 
the  surface,  is  roasted  off,  and  is  strongly  oxidized  by  the  lead 
oxide  formed  at  the  same  time.  During  the  oxidation  slag  is 
formed  from  the  edges  of  the  scorifier,  by  the  combination  of  an- 
other part  of  the  lead  oxide  with  the  metallic  oxides  and  earths 
that  are  present,  and  with  the  borax.  The  time  required  for  this 
first  heating  (roasting  and  fusing)  is  from  25  to  30  minutes  when 
a  completely  fused  ring  of  slag,  without  adherence  to  the  edge  of 
the  scorifier,  will  show  itself.  (Refractory  ores,  such,  for  instance, 
as  contain  zinc,  cobalt,  and  nickel,  or  which  contain  considerable 
lime,  require  the  strongest  heat,  and,  should  they  not  completely 


SILVER — ASSAYS   FOR   NON-ALLOYS.  133 

fuse  even  then,  a  sufficiently  large  addition  of  borax  must  be  made 
before  the  final  heating.)  The  second  period  is  that  of  the 
"scarification."1  The  fire  is  checked,  and  the  mouth  of  the  muffle 
is  opened,  until,  by  the  continued  oxidation  of  the  lead  and  for- 
eign metallic  compounds,  the  entire  surface  of  the  lead  is  covered 
with  slag.  This  will  require  from  20  to  30  minutes.  The  mouth 
of  the  muffle  is  then  closed,  the  heat  raised,  and  a  final  heating 
of  10  to  15  minutes  is  given  to  render  the  slag  completely  fluid. 
The  scorifier  is  now  taken  from  the  furnace,  and  allowed  to  cool 
in  the  scorifier  or  poured  off.  After  cooling  off,  the  lead  button 
is  carefully  freed  from  slag  and  hammered  into  the  form  of  a  cube, 
with  truncated  edges  and  corners.  The  time  required  for  the 
entire  operation  will  be  from  f  to  1 J  hours,  according  to  the  de- 
gree of  fusibility  of  the  ores.  When  the  ores  are  very  poor,  a 
number  of  the  lead  buttons  which  have  been  obtained  are  placed 
on  a  scorifier,  either  with  or  without  borax,  and  scorified  as  indi- 
cated above.  If  necessary  the  concentration  is  repeated  until 
finally  one  button  containing  the  entire  percentage  of  silver  is 
obtained.  A  second  scorifi cation  is  also  advisable,  in  case  the 
button  be  too  large,  or  when  it  contains  much  antimony,  arsenic,  or 
copper.  A  percentage  of  nickel  will  exert  a  disturbing  influence 
in  cupellation.  A  cupel  will  usually  absorb  about  its  own  weight 
of  litharge,  from  which  the  proper  size  of  the  button  may  be 
estimated. 

Hungary:2  Two  samples  each  of  2.5  grammes  (about  ^  A.  T.) 
are  each  charged  with  8  to  16  parts  of  granulated  lead,  in  such 
a  manner  that  one-third  of  it  is  mixed  with  the  ore  and  some 
silver  flux  (2  parts  of  melted  Villach  litharge  and  1  part  of  cal- 
cined borax),  and  covered  with  the  remaining  two-thirds.  Lower 
Ila-fz :  5  grammes  (about  J  A.  T.)  are  mixed  in  the  scorifier  with 
50  grammes  of  granulated  lead  and  0.75  to  1  gramme  of  borax, 
and  covered  with  0.5  gramme  of  borax.  The  cupels  consist  of  3 
parts  wood-ash  and  1  part  bone-ash. 

With  chloridized  ores :  A  charge  of  5  to  10  grammes  (J  to  J 
A.  T.)  of  the  ore  is  scorified  with  ten  times  its  weight  of  lead, 

[»  Percy's  Metallurgy  of  Silver  and  Gold,  vol.  i.  pp.  242-244.— G.] 
2  B.  u.  h.  Ztg.,  1871,  p.  254. 


134  ASSAYING. 

and  cupelled  to  determine  the  percentage  of  silver.  In  a  second 
sample  the  silver  chloride  is  dissolved  out  by  lixiviation  with 
sodium  hyposulphite,  and  the  residue  is  scorified,  etc.,  for  the 
estimation  of  the  unchloridized  silver. 

2.  Crucible  assay} — In  this  method  of  assaying,  the  ore  is 
fused  with  lead  oxide  (litharge,  white  lead),  in  order  to  decom- 
pose the  metallic  sulphides  (p.  76),  with  fluxing  agents  (potash, 
borax),  for  slagging  off  oxide  and  earths,  and  with  some  carbo- 
naceous substance  (charcoal  powder,  flour,  argol,  black  flux),  for 
reducing  the  lead  which  then  collects  the  silver.  The  quantity 
of  the  reducing  agent  will  depend  on  the  reducing  power  of  the 
ore.  It  should  be  so  gauged  that  the  lead  button  produced  shall 
not  be  too  large  in  order  to  prevent  a  notable  loss  of  silver  in 
cupellation.  Ores  containing  a  large  percentage  of  antimony, 
arsenic,  and  zinc  should  be  previously  roasted,  to  prevent  the 
formation  of  oxysulphides,  etc.,  which  are  difficult  to  decompose, 
and  which  carry  silver  along  with  them  into  the  slag ;  5  grammes 
(about  ^  A.  T.)  of  the  finely  powdered  ore  are  mixed  in  a  crucible 
with  40  grammes  of  a  flux  consisting  of  1.5  parts  of  litharge, 
0.15  part  of  potassium  carbonate,  and  0.08  part  of  flour.  This 
is  covered  with  25  grammes  of  litharge,  and  this  in  turn  with 
about  4  grammes  of  borax.  The  crucible  should  have  smooth 
sides,  a  diameter  of  45  millimeters  at  the  top,  and  of  30  milli- 
meters at  the  bottom,  an  inside  height  of  145  millimeters,  and 
outside  of  165  millimeters.  The  charged  crucible  is  then  placed 
in  the  furnace  upon  a  bed  of  glowing  coke,  which  should  cover 
the  grate  to  a  height  of  from  100  to  150  millimeters,  and  is  then 
surrounded  up  to  its  rim  with  wood  charcoal.  The  furnace  is 
left  open  for  the  first  quarter  of  an  hour.  After  the  coal  has 
been  replenished,  the  cover  of  the  furnace  is  put  on  and  the 
fusing  is  continued  for  a  quarter  of  an  hour  longer.  The  crucible 
is  then  taken  out,  allowed  to  cool,  and  the  lead  button,  which 
should  weigh  from  20  to  25  grammes,  is  freed  from  slag.  (Chili.) 
The  same  quantity  of  litharge  as  used  for  the  assay  is  fused  at 
the  same  time,  but  without  ore,  with  fluxing  agents.  The  lead 
button  is  freed  from  slag  and  cupelled,  to  determine  the  percent- 

[i  Percy's  Metallurgy  of  Silver  and  Gold,  vol.  i.  pp.  244-248.— G.-] 


SILVER — ASSAYS  FOR  NON-ALLOYS.  135 

age  of  silver,  which  must  be  deducted  from  the  assay-button. 
Or,  5  grammes  (about  \  A.  T.)  of  ore  are  fused  with  50  grammes 
of  litharge,  2  grammes  of  argol,  12  grammes  of  sodium  carbo- 
nate, with  a  covering  of  common  salt,  and  the  resulting  lead  but- 
ton is  cupelled.  White  lead  is  sufficiently  free  from  silver. 

Mexican  charge:1  20  grammes  (about  f  A.  T.)  of  ore,  66 
grammes  of  litharge,  the  same  quantity  of  sodium  carbonate, 
and  3  grammes  of  charcoal  powder  are  mixed  in  a  crucible  of 
the  above  dimensions  and  covered  with  20  grammes  of  common 
salt.  40  assays  are  put  in  the  furnace  and  fused,  first,  for  a 
quarter  of  an  hour,  during  which  the  furnace  is  left  open.  It  is 
then  closed,  and  the  assays  are  fused  for  half  an  hour  longer. 
66  grammes  of  litharge  are  reduced,  and  the  amount  of  silver 
found  is  deducted. — Another  charge  is  as  follows:  16  grammes 
(246.92  grains,  about  J  A.  T.)  of  ore,  48  grammes  of  litharge,  60 
grammes  of  sodium  carbonate,  16  to  20  grammes  of  powdered 
charcoal,  which  is  omitted  when  a  large  percentage  of  iron  py- 
rites is  present. — Another  charge  is :  2  grammes  (about  -j1^  A.  T.) 
of  ore,  25  grammes  of  litharge,  10  grammes  of  sodium  carbonate, 
and  a  covering  of  common  salt. — Spain:2  5  grammes  (77.16 
grains,  about  ^  A.  T.)  of  ore  are  fused  in  a  crucible  with  20 
grammes  of  litharge,  borax,  black  flux,  or  potassium  carbonate 
and  flour,  with  a  covering  of  common  salt. — English  charge:  10 
grammes  (154.32  grains,  about  J  A.  T.)  of  ore,  the  same  quantity 
of  sodium  carbonate,  50  grammes  (771.61  grains)  of  litharge, 
and  1  to  1.5  grammes  of  argol,  with  a  covering  of  10  grammes 
of  common  salt  and  the  same  quantity  of  borax. —  Gold  and  silver 
sweepings:  10  grammes  of  borax  and  the  same  quantity  of  argol 
are  poured  into  a  crucible  with  smooth  sides,  75  millimeters  in 
diameter  on  the  top,  and  110  millimeters  high;  upon  this  are 
placed  20  grammes  of  litharge.  The  sides  of  the  crucible  are 
moistened  by  gently  breathing  upon  them,  it  is  then  inclined  and 
turned  in  such  manner  that  litharge  adheres  to  the  sides  about 
f  the  way  up.  15  grammes  of  potassium  carbonate  and  25 
grammes  of  sweepings  are  then  added,  and  the  entire  mass  is 
thoroughly  mixed  together  with  a  broad  spatula.  It  is  then  cov- 
ered with  10  grammes  of  sodium  carbonate,  and  upon  this  comes 

i  B.  u.  h.  Ztg.  1874,  p.  86.  2  B.  u.  h.  Ztg.  1868,  p.  26. 


136  ASSAYING. 

a  layer  of  common  salt  12  millimeters  thick,  and  finally  5 
grammes  of  litharge  are  strewed  around  the  sides  of  the  crucible. 
The  furnace  is  filled  with  pieces  of  gas-coke  the  size  of  a  walnut, 
the  coke,  when  it  is  in  a  glow,  is  stamped  down,  and  from  6  to  8 
crucibles  are  placed  in  the  fire  in  such  a  manner  that  the  edge  of 
the  crucible  projects  but  little  above  the  coke.  The  furnace  is 
then  closed,  and  the  heat  gradually  increased  until  the  charge 
ceases  to  swell  up.  The  temperature  is  then  quickly  raised  for 
from  15  to  20  minutes,  until  the  charges  have  become  thin  fluid 
and  flow  bright  and  uniform.  The  operation  is  therefore  finished 
in  about  half  an  hour.  The  crucibles  are  now  allowed  to  cool, 
and  the  buttons  weighing  about  22  grammes  are  freed  from  slag 
and  then  cupelled.  (In  assays  of  large  lots  of  ore  five  assays  are 
made.) — Other  charges  for  sweepings:  25  grammes  (about  |-  A.  T.) 
of  sweepings,  the  same  quantity  of  minium,  35  grammes  of  flux 
(prepared  by  mixing  600  parts  of  potassium  carbonate,  200  parts 
borax,  100  parts  glass-galls,  100  parts  soda,  30  parts  saltpetre,  30 
parts  powdered  charcoal);  or,  25  grammes  of  sweepings,  20 
grammes  of  common  salt,  the  same  quantity  of  sodium  carbonate 
and  of  potassium  carbonate,  25  grammes  of  litharge,  10  grammes 
of  argol,  and  the  same  quantity  of  powdered  glass;  or,  25 
grammes  of  sweepings,  20  grammes  of  litharge,  25  grammes  of 
flux  (1  part  potassium  carbonate  and  1  sodium  carbonate),  and  a 
covering  of  common  salt.  The  charge  is  kept  in  the  furnace 
until  quiet  fusion,  requiring  about  three-quarters  of  an  hour 
(Braubach). — Slags:  10  grammes  (about  J  A.  T.)  of  slag,  150  to 
160  grammes  of  litharge,  2.5  grammes  of  quartz,  and  0.25 
gramme  of  charcoal  powder.  The  charge  is  fused  in  a  crucible 
for  20  minutes  after  the  development  of  gas  in  the  furnace  has 
ceased,  and  the  buttons  of  two  charges  are  cupelled  together 
(Pribram). — Freiberg:  7.5  grammes  (about  J  A.  T.)  of  slag  are 
mixed  in  a  crucible  with  11  to  15  grammes  of  potassium  carbon- 
ate and  flour,  19  to  30  grammes  of  granulated  lead  are  strewed 
on  top,  and  the  charge  is  fused  for  3  hours  in  the  furnace. — Refuse 
from  stamping  mills:  10  grammes  (about  J  A.  T.)  of  substance 
are  mixed  in  a  high  crucible  (Fig.  49,  p.  64)  with  60  to  120 
grammes  of  potassium  carbonate  and  flour;  upon  this  is  placed 
50  to  100  per  cent,  of  borax,  next  10  to  15  grammes  of  granu- 


SILVER — ASSAYS   FOR   NON-ALLOYS.  137 

lated  lead,  and  finally  a  covering  of  common  salt.     It  is  fused  in 
the  muffle-furnace  for  1J  to  2  hours. 

According  to  Gorz,1  the  results  obtained  in  assaying  sweepings 
and  other  refuse  from  the  manufactures  of  silverware  frequently 
show  great  variations. — This  is  due  largely  to  the  method  adapted 
for  the  assay,  and  also  to  the  heterogeneous  character  of  the  ma- 
terial, which  sometimes  contains  several  per  cent,  of  mechanically 
mixed  carbon.  The  gold  and  silver  are  usually  present  in  the  me- 
tallic state ;  only  the  refuse  from  smelting  works  contains  chloride 
of  silver. 

The  following  observations  are  recorded  by  Gorz  : — 

1.  In  samples  rich  in  metal  and  poor  in  carbon  by  the 

Scorification  assay.  Crucible  assay. 

8.296  silver  {    8'270 

I    8.000 

iiS 

10.555  10.490 

10.847  10.400 

12.645  12.300 

59.775  54.920,  an   impure  chlo- 

ride of  silver 

9.753  {   9'680 

I   9.750 

9.366  9.190 

10.630  9.790 

0.028  gold  0.024 

2.  In  samples  poor  in  metal  and  rich  in  carbon  by  the 

Scorification  assay.  Crucible  assay. 

0.322  silver  0.315 

1.370  silver 


1.364  silver 
0.021  gold 


0.390  silver 
0.022  gold 


0.021  gold 
1.348  silver 
0.020  gold 
0.400  silver 
0.0207  gold 
0.386  silver 


0.023  gold 

f  0.316  silver  f  0.276  silver 

I  0.075  gold  I  0.079  gold 

f  0.338  silver  f  0.345  silver 

\  0.336  gold  t  0.340  gold 

J  0.164  silver  f  6.132  silver 

1 0.063  gold  I  0.068  gold 

1  Bg.  u.  Httumsch,  Ztg.  1886,  p.  441. 


138  ASSAYING. 

From  the  foregoing  it  will  be  observed  that  with  rich  sweep  con- 
taining no  carbon  the  highest  results  are  obtained  by  the  scorifica- 
tion  assay,  and  with  poor  sweep  containing  carbon  the  crucible 
assay  gives  the  best  results.  Hence,  every  substance  rich  in  noble 
metals,  containing  no  carbon  and  holding  the.  metal  chemically 
fixed,  should  be  tested  by  the  scorification  assay,  and  every  sub- 
stance strongly  contaminated  with  carbon  by  the  crucible  assay. 
Lead  assaying  crucibles  are  recommended  for  the  latter  on  account 
of  their  narrowing  towards  the  top ;  thus  loss  by  sputtering  is 
avoided  as  much  as  possible. 

3.  Combined  lead  and  silver  assay. — This  method  of  assaying 
is  used  for  oxidized  lead  products  (litharge,  skimmings,  dross), 
and  for  galena  with  at  least  30  to  40  per  cent,  of  lead,  and  not 
over  0.12  per  cent,  of  silver.  Such  galena,  after  the  assay  with 
potassium  carbonate,  as  described  on  page  87,  is  fused  to  a  lead 
button,  which  is  then  cupelled.  This  method  is  not  satisfactory 
after  the  preliminary  assay  with  iron  (pp.  81,  82),  as  the  iron  sul- 
phide will  retain  silver  in  varying  quantities  in  the  slag. 
.  Litharge:  20  grammes  (about  f  A.  T.)  litharge,  15  grammes 
potassium  carbonate  and  flour,  and  5  to  6  per  cent,  of  powdered 
charcoal,  with  a  covering  of  common  salt,  are  placed  in  a  crucible 
and  fused  in  the  muffle-furnace.  Jf  necessary,  several  of  the 
buttons  are  concentrated  by  scorification  (p.  133)  and  cupelled. 
Skimmings  and  dross  are  charged  in  the  same  manner ;  but,  should 
they  be  very  impure,  the  lead  buttons  must  be  scorified  with  4  to 
8  times  their  weight  of  granulated  lead  before  they  are  cupelled. 

B.  Cupellation  of  the  argentiferous  lead  (assaying  by  the  cupel  or 
cupellatiori).1 — The  lead  buttons  obtained  according  to  A  Nos.  1 
to  3  (pp.  129-138)  are  subjected  to  oxidizing  fusion.  During  this 
operation  the  lead  is  first  oxidized ;  the  lead  oxide  yields  up 
oxygen  partly  to  the  foreign  metals,  and  partly  combines  with 
their  oxides ;  and  if  they  are  not  too  refractory  (as,  for  instance, 
ferric  and  stannic  oxide,  etc.),  enters  with  them  into  the  cupel. 

If  the  lead  contains  much  antimony  and  zinc,  it  is  apt  to  cause 
cracks  in  the  cupels ;  copper  colors  them  green,  and  the  percent- 

C1  Percy's  Metallurgy  of  Silver  and  Gold,  vol.  i.  pp.  279-282.] 


SILVEE — ASSAYS   FOR   NON-ALLOYS.  139 

age  of  copper  may  be  quantitatively  determined  within  certain 
narrow  limits  by  the  intensity  of  the  color. 

The  cupels  (Fig.  54,  p.  66),  first  carefully  wiped  out  with  the 
fingers,  then  all  extraneous  matter  blown  out,  are  thoroughly 
heated  (ignited)  in  the  muffle.  They  are  arranged  in  two  rows, 
six  in  each  row,  in  the  front  third  of  the  muffle.1  The  lead  but- 
tons are  now  laid  hold  of  with  a  pair  of  tongs  (Fig.  59,  p.  72) 
and  gently  deposited,  first  in  the  front  and  then  in  the  back  row 
of  crucibles.  The  mouth  of  the  muffle  is  closed,  the  fire  is  urged 
on,  and  the  lead  fused  as  quickly  as  possible.  The  lead  will  at 
first  be  covered  with  a  dull,  dark  film.  As  soon  as  this  disap- 
pears, and  the  lead  shows  a'lustrous,  fuming  surface,  the  mouth 
of  the  muffle  is  opened  (with  the  exception  of  a  low  piece  of 
charcoal  which  is  left  in  it)  for  the  admission  of  air  to  oxidize 
the  lead,  and  the  temperature  is  lowered,  by  ceasing  to  stir  the 
fire,  to  lessen  the  loss  of  silver.  Cojd  scorifiers  are  placed  in 
several  rows  above  each  other  back  of  the  cupels,  and,  if  the 
argentiferous  lead  is  very  rich,  the  cooling-iron  (Fig.  61,  p.  72), 
which  should  be  frequently  cooled  off  in  water,  is  moved  -  to  and 
fro  closely  over  the  cupels.  The  correct  temperature  is  indicated 
by  the  rising  lead  fumes  whirling  over  the  assays,  and  not  slowly 
creeping  over  them  or  rising  straight  up ;  by  the  cupels  glowing 
dark  brown,  by  small  scales  of  crystallized  litharge  (plumose 
litharge,  Federglatte)  showing  themselves  on  the  inner  edge,  and 
by  a  bright  but  not  too  wide  border  of  litharge  upon  the  lead. 
If  the  temperature  is  too  low,  the  fume  creeps  slowly  over  the 
cupels ;  these  become  too  dark,  a  dark  rim  of  litharge  is  formed, 
and  the  lead  ceases  to  "drive."  This  is  called  a  "freezing"  of 
the  assay.  Frozen  assays,  if  again  brought  to  "driving"  by  a 
higher  heat,  and  generally  some  addition  of  lead,  cause  a  con- 
siderable loss  of  silver.  By  too  high  a  temperature,  the  lead 
fumes  rise  up  straight,  the  cupels  glow  too  brightly,  neither 
plumose  litharge  (Federglatte)  nor  a  rim  of  litharge  shows  itself, 
and  the  loss  of  silver  increases.  At  the  correct  temperature  small 
beads  of  litharge  float  upon  the  surface  of  the  lead  button,  the 

1  Hempel's  gas-furnace  with  oxidizing  apparatus  in  Fresenius's  Ztschr. 
xvi.  454;  xviii.  404. 


1 40  ASSAYING. 

heat  to  which  it  is  subjected  causing  convection  currents,  which 
give  the  button  a  motion  from  below  upwards  ("  driving"),  and 
a  convex  surface  from  which  the  luminous  beads  and  patches  of 
litharge  are  continually  thrown  towards  the  sides,  are  there  ab- 
sorbed by  the  cupel.  As  soon  as  these  patches  upon  the  dimin- 
ishing lead  become  larger  towards  the  end,  the  scorifiers,  which 
had  been  placed  back  of  the  cupels,  are  removed,  the  cooling  with 
the  cooling-iron  is  stopped,  and  the  fire  is  urged  on.  Towards 
the  end  the  last  of  the  lead  is  absorbed,  and  the  silver  button 
presents  itself  colored  with  all  the  tints  of  the  rainbow  (brightening, 
coruscation),  which  gradually  disappear,  whereupon  the  button 
solidifies.  (If  the  temperature  has  been  too  low,  the  surface  of 
the  button  is  dull  and  yellow,  and  the  unabsorbed  litharge  forms 
lumps  or  scales  about  it ;  while  otherwise,  it  is  pure  silver-white 
on  top  and  bottom,  and  very  lustrous.)  If  the  bead  is  large  the 
cupels  are  allowed  to  cool  off  slowly  by  drawing  them  to  the  front 
of  the  muffle,  to  prevent  the  buttons  from  "sprouting"  or  "spitting" 
They  are  then  taken  out  upon  a  piece  of  sheet-iron,  and  the 
buttons  (generally  of  99.7  to  99.8  per  cent,  pure  silver)  are  de- 
tached by  means  of  a  pair  of  pliers  (p.  74),  and  brushed  off 
with  the  button-brush  (p.  74).  Faultless  buttons  brightened  at  a 
sufficiently  high  temperature  (smaller  ones  are  round,  larger  ones 
hemispherical)  should  have  a  silvery  lustre  on  the  surface,  be  dull 
silver-white  and  crystalline  on  the  bottom,  and  without  rootlets. 
They  are  then  weighed.  The  globule  of  silver  obtained  from 
the  separately  scorified  and  cupelled  granulated  lead,  if  not 
entirely  free  from  silver,  is  placed  in  a  scale-pan  containing  the 
weights ;  or,  the  silver  percentage  of  the  lead  having  been 
determined  once  for  all,  it  may  be  deducted  from  the  results 
obtained. 

Assays  of  silver  should  agree  very  closely,  and  if  properly 
conducted  are  of  great  accuracy.  The  results  of  duplicate  assays 
should  not  differ  from  each  other  more  than  one-half  ounce  Troy 
per  ton  of  two  thousand  pounds.  Should  a  greater  difference  be 
found,  an  additional  assay  should  be  made. 

Smaller  losses  of  silver  occur  in  scorifying  (which  for  this 
reason  should  be  continued  as  long  as  possible,  so  as  to  obtain 
small  lead  buttons  requiring  but  a  short  time  for  "  driving")  than 


SILVER — ASSAYS   FOR  XON- ALLOYS.  141 

iii  cupelling,  by  the  volatilization  of  silver,  and  by  the  silver 
oxide  passing  into  the  cupel  with  the  lead  oxide  by  which  it  has 
been  oxidized  (loss  by  cupellation,  Kapellenzug).  The  loss  in- 
creases with  the  temperature  and  the  size  of  the  button,  and  for 
this  reason,  with  the  time  required  for  cupelling,  as  well  as  with 
the  porosity  of  the  cupels.  The  percentage  of  loss  is  considerably 
larger  (2  to  4  per  cent.)  in  smaller  buttons  (poorer  ores)  than  in 
larger  buttons  (1  to  If  per  cent.),  but  in  the  first  case  can  gene- 
rally not  be  determined  by  the  balance.  The  smallest  loss  occurs 
in  gas  muffle-furnaces  (Fig.  31,  p.  50),  which  have  no  vent-holes 
in  the  muffle.  In  case  the  ore  contains  tellurium,  the  button 
spots  at  the  moment  of  solidification,  after  brightening,  and  fine 
globules  of  the  metal  are  thrown  off  and  lost. 

Assay  of  native  silver  ores. — The  following  method  is  recom- 
mended by  Lowe.1  When  silver  is  chemically  combined  in  the  ore 
it  is  not  difficult  to  determine  its  assay  value,  but  in  ores  containing 
the  silver  in  the  metallic  state,  the  assay  can  yield  only  approxi- 
mate results.  The  following  method  obviates  this  difficulty  to  some 
extent.  The  ore  is  coarsely  powdered  and  sampled  down  to  a 
half-pound  (226.704  grammes),  then  finely  powdered  and  passed 
through  a  100-mesh  sieve.  The  sifted  ore  is  divided  into  four  parts 
and  four  assays  made  of  it,  each  amount  for  each  assay  being 
taken  as  nearly  as  possible  from  the  same  relative  parts  of  each 
quarter.  The  average  of  the  four  assays  is  taken  as  the  result. 
The  metallic  particles  or  scales  of  silver  which  will  not  pass  through 
the  meshes  of  the  sieve  are  mixed  with  assay  lead,  cupelled,  and  the 
weight  of  the  resulting  button  reduced  to  its  proper  value  added  to 
the  result  obtained  from  the  assay  of  the  sittings. 

Examination  of  lead  ores  for  traces  of  silver. — According  to 
Krutzvvig,2  20  to  25  grammes  of  galena  are  fused  with  a  mixture 
of  tartar,  soda,  and  borax  in  an  iron  crucible.  The  reduced  lead 
dissolved  out  with  HN03  free  from  chlorine,  dilute  the  solution,  and 
filter  off  any  lead  sulphate  formed.  Precipitate  from  the  filtrate 
the  iron,  lead,  and  argentic  peroxide  of  lead  with  excess  of  caustic 
so'da.  Separate  the  precipitate  by  decantation,  wash  thoroughly 
with  an  addition  of  ammonia,  evaporate  to  dryness  and  take  up 

1  Engineering  and  Mining  Journal,  Sep.  24,  1881,  p.  203. 

2  Chemikerztg,  1882,  p.  1206  ;  Montanztg,  1882,  p.  2. 


142  ASSAYING. 

with  HN03.  Remove  the  lead  from  this  solution  with  H2S04  and 
examine  the  filtrate  for  silver  with  HC1.  Instead  of  HC1,  caustic 
soda  may  be  added  which  in  the  presence  of  silver  produces  an 
intensely  yellow  precipitate  of  argentic  peroxide  of  lead. 

II.   Wet  Assays. 

i 

Sailing's  volumetric  assay.1 — 2  to  5  grammes  of  galena  are 
fused  in  a  porcelain  crucible  with  3  or  4  times  its  weight  of  a 
mixture  of  equal  parts  of  saltpetre  and  soda.  This  is  allowed  to 
cool  off;  the  contents  of  the  crucible  are  lixiviated  with  water, 
heated  in  a  porcelain  dish,  and  filtered.  The  residue  is  decom- 
posed with  diluted  nitric  acid,  and  evaporated  to  dryness.  The 
dry  mass  is  then  taken  up  with  water  acidulated  with  nitric  acid, 
heated  and  filtered.  Ferric  sulphate,  or  iron-alum  is  added  to 
the  cooled-off  filtrate,  and  it  is  then  titrated  with  a  TQ-  normal 
solution  of  ammonium  sulpho-cyanide,  which  is  prepared  by  dis- 
solving 0.7  to  0.75  gramme  of  the  salt  in  1  liter  of  water.  The 
titer  is  made  to  correspond  Avith  a  silver  solution  of  known 
strength,  in  such  a  manner  that  1  cubic  centimeter  of  the  ammo- 
nium sulpho-cyanide  solution  corresponds  exactly  to  1  cubic  cen- 
timeter of  silver  solution.  The  latter  is  obtained  by  dissolving  1 
gramme  of  chemically  pure  silver  in  nitric  acid,  and  diluting  it 
to  a  bulk  of  1  liter.  The  presence  of  copper  in  small  quantities 
is  not  injurious,  and  of  that  of  lead  is  rather  favorable,  as  the 
white  precipitate  of  lead  sulphate,  which  is  formed  after  the  ferric 
sulphate  has  been  added,  makes  the  recognition  of  the  final  reac- 
tion sharper.  A  large  percentage  of  iron  gives  a  brownish  col- 
ored solution,  which  does  not  permit  a  distinct  recognition  of  the 
final  reaction.  Larger  quantities  of  copper  must  be  previously  re- 
moved, but  cobalt  and  nickel,  if  the  operator  has  some  experi- 
ence, admit  of  an  easy  recognition  of  the  final  reaction  by  a  yel- 
lowish brown  color.  The  assay  requires  about  three  hours,  and 
may  be  especially  recommended  when  no  muffle-furnace  is  at 
hand,,  or  if  only  one  sample  is  to  be  assayed  for  which  it  would  not 
be  worth  while  to  heat  a  furnace.  The  permissible  error  allowed 

1  Fresenius's  Ztschr.  xiii.  171  ;  Oestr.  Ztschr.  1879,  No.  27. 


SILVER — ASSAYS   FOR   NON-ALLOYS.  143 

iii  the  smelting  works  at  Pribram  is  0.03  per  cent,  from  ores  car- 
rying 0.30  to  0.60  per  cent,  of  silver,  and  the  differences  obtained 
by  this  assay  vary  within  narrower  limits  than  those  allowed  for 
dry  assays.  The  assays  give  equally  good  results  for  all  degrees 
of  richness,  if  the  galena  is  pure  and  contains  but  little  iron. 

32.    ASSAYS  OF  ALLOYS. 

These  are  generally  executed  by  the  wet  method  only  for  silver 
containing  copper  (as,  for  instance,  coins).  The  dry  method  is 
mostly  used  for  other  alloys,  and  they  are  either  assayed  by  direct 
cupellation  without  sc'orification,  with  an  addition  of  lead  in  case 
the  sample  does  not  already  contain  a  sufficient  quantity. 
-  A.  Dry  assays. 

1.  Lead  bullion.1 — 10   to   20   grammes,  according  to  the  per- 
centage of  silver  in  it,  are  directly  worked  off  on  the  cupel ;  but 
if  the  lead  is  impure  (slag  lead,  zinciferous  lead),  it  must  be  pre- 
viously scorified.     Poor  lead   is   slagged  off  on  the  scorifier  in 
quantities  of  from  40  to  50  grammes,  and  the  resulting  buttons 
are   concentrated   into   one   button  by  scorifying  them  once  or 
several  times,  and  the  collected  button  thus  obtained  is  cupelled. 
(For  instance,  10  assays  of  50  grammes  each  of  Pattison's  granu- 
lated lead,  which  is  very  poor  in  silver,  are  concentrated  to  one 
button.)   The  cupels  used  for  a  charge  of  from  10  to  20  grammes 
of  granulated  lead,  have  an  outer  diameter  of  49  millimeters  on 
the  top  and  39  millimeters  on  the  bottom,  a  clear  width  of  37 
millimeters,  a  total  height  of  23  millimeters,  and  a  depression  of 
17  millimeters. 

2.  Silver  amalgam. — 5  grammes  of  the  assay  sample  are  weighed 
off  in  a  watch-glass,  and  gradually  heated  in  the  cupel  for  1J 
hours  in  a  moderately  heated  muffle.     After  all  the  mercury  is 
volatilized,  6  or  7  times  the  quantity  of  lead  is  added  and  the 
charge  cupelled. 

3.  Copper  poor  in  silver  (black  copper,  refined  copper). — 2.5 
grammes  are  scorified  with  18  to  20  times  the  quantity  of  lead 
and  cupelled,  whereby  the  cupel  will  be  colored  dark  green.    Pure 

i  Abtreiben  mit  Sauerstoff  in  B.  u.  h.  Ztg.  1868,  p.  351. 


144  ASSAYING. 

or  plumbiferous  copper  may  also  be  immediately  cupelled  with  16 
to  18  times  the  quantity  of  lead  in  one  charge. 

4.  Cupriferous  silver  or  fine  silver*  (coins,  refined  silver,  etc.). — 
The  sample  is  directly  cupelled  (mint  assay)  with  a  quantity  of 
lead  free  from  silver  (simple  weights  of  lead  in  the  form  of  small 
sticks  or  round  or  half-round  pieces  are  used,  but  not  granulated 
lead),  corresponding  to  the  percentage  of  copper.  Smaller  and 
finer  cupels  (mint  cupels)  are  used.  They  consist,  like  the  French 
cupels,  either  of  powdered  bone-ash  alone,  or  of  bone-ash  and 
lixiviated  wood-ash,  which  makes  them  more  porous.  They  are 
placed  in  a  small  muffle-furnace  (mint  or  fine  assay  furnace,  Fig. 
28,  p.  54),  for  the  better  regulation  of  the  heat ;  or  what  is  still 
better,  in  a  gas-furnace  (Fig.  31,  p.  50).  Where  the  percentage 
of  silver  is  not  known,  the  approximate  percentage2  is  first  deter- 
mined by  a  preliminary  assay  (cupelling  with  16  times  the  quan- 
tity of  lead,  or  by  the  touchstone),3  so  that  the  proper  quantity 
which  experience  has  proven  to  cause  the  smallest  loss  of  silver 
may  be  used.  With  silver  coins,  in  which  the  silver  percentage 
is  known,  the  preliminary  assay  is  unnecessary. 

The  numbers  given  in  the  following  table  may  be  taken  as  a 
guide : — 

Degree  of  fineness  of  the  alloy.  Multiples  of  lead. 

Silver  in  thousandth  parts. 

1000  to  950 4 

950  "  900 6 

900  "  850 8 

800  "750 12 

750  "  650     .         .         .         .        .        .14 

600  "      0 16  to  17 

1  Probe  iiber  der  Larape  in  Fresenius's  Ztsclir.  1879,  p.  82.    ' 

2  Coins :  The  German  Reiclismark,  German  Thaler,  Austrian  and  South 
German  Gulden,  900  thousandth  parts  Ag  ;  English  silver  coins,  925  ;  French 
small  silver  coins,  835  ;  5,  2,  1,  |,  £  franc  pieces,  900  ;  German  nickel  coins, 
75  Cu  and  25  Ni ;  German  copper  coins,  96  Cu,  3  Su,.l  Zu ;  American  silver 
coins,  900  ;  American  nickel  coins,  75  Cu  and  25  Ni ;  American  copper  coins, 
95  Cu,  3  Sn,  2  Ni ;  French  small  coins  (5  cent.),  95.21  Cu,  3.18  Sn,  0.44  Zn, 
0.25  Ni,  0.58  Pb,  0.06  Ag.    Swiss  coin  (5  cent.),  Cu  58.920,  Zn  23.700 ;  Ni  11.561, 
Ag  5.146,  Pb  0.326,  Co  0.286. 

3  Dingier,  cxxiii.  366  ;  Ann.  de  Chemie  et  Phya.  1875  ;  Bay,  Ind.  u.  Gew. 
Bl.  1869,  p.  130;    Kick,  techn,  Bl.  1873,  p.  35;  Fresenius's  Ztschr.  1878, 
p.  142. 


SILVER — ASSAYS  OF  ALLOYS.  145 

A  sample  of  the  alloy  to  be -assayed,  weighing  0.5  gramme, 
is  hammered  out  and  cut  up  into  fine  shreds.  Generally  two 
assays  are  made  at  one  time.  The  samples  from  bars  are  taken 
from  the  upper  and  lower  sides,  and  are  obtained  from 
pieces  weighing  about  2.5  grammes,  which  have  been  cut  out 
from  the  lo\ver  and  upper  sides  of  the  bar  on  opposite  ends. 
The  samples  are  wrapped  up  in  cornets  of  fine  letter-paper,  and 
placed  upon  a  small  assay-plate.  When  lead  granules  are  not  at 
hand,  a  piece  of  stick  lead  is  weighed  out  and  placed  in  two 
thoroughly  glowed-out  cupels,  standing  in  the  centre  of  the 
strongly  heated  muffle-furnace  (Fig.  30,  p.  49).  The  Paris  mint 
cupels  have  been  especially  recommended  for  the  purpose.  Their 
outer  diameter  is  26  millimeters  on  the  top,  and  22  millimeters 
on  the  bottom ;  clear  width,  21  millimetres  ;  total  height,  14  mil- 
limeters, with  a  depression  of  8  millimeters.  The  mouth  of  the 
muffle  is  closed  with  a  coal,  and  as  soon  as  the  lead  "  drives"  the 
cornet  containing  the  sample  is  placed  in  the  cupel,  the  mouth  of 
the  muffle  again  closed,  and  the  assay  allowed  to  "  drive."  The 
mouth  of  the  muffle  is  now  again  opened,  with  the  exception  of 
a  low  piece  of  coal  or  small  piece  of  iron,  the  cupels  are  drawn 
forward  towards  the  mouth  of  the  muffle  and  the  temperature 
is  lowered  by  partly  closing  the  draught  of  the  furnace,  or  also 
by  cooling  with  a  small  cooling-iron  (Fig.  61,  p.  72),  until  a  small 
ring  of  litharge  and  some  plumose  litharge  (Federglatte)  appear. 
The  assays  are  now  gradually  pushed  back,  and  the  temperature  is 
raised  by  opening  the  draught  of  the  furnace,  so  that  the  assay 
may  "  brighten"  sufficiently  hot,  during  which  the  ring  of  litharge 
will  disappear,  but  the  plumose  litharge  (Federglatte)  remain.  The 
cupels  are  now  drawn  forward  towards  the  mouth  of  the  muffle, 
and  allowed  gradually  to  cool  off  to  prevent  "  spitting."  When 
sufficiently  cool  they  are  taken  from  the  muffle,  and  the  buttons 
are  removed  by  means  of  a  pair  of  pincers  and  brushed.1  In 
successful  assays  the  surface  of  the  button  is  smooth,  writh  a 
silvery  lustre  on  the  top,  and  a  dull  silver- white  color  on  the 
bottom.  If  the  operation  has  been  conducted  at  too  low  a  tem- 

1  [The  button  should  be  strongly  squeezed  with  the  pincers  to  detach  any 
adhering  particles  of  bone-ash  or  oxide. — G.] 
10 


146  ASSAYING. 

perature,  the  surface  is  dull,  and  has  a  bluish  tint,  aud  the  bottom 
is  covered  with  a  yellowish  or  greenish  coating  of  lead  oxide.  If 
the  temperature  has  been  too  high,  the  button  is  dull  in  some 
places,  very  lustrous  in  others,  the  surface  is  sunken,  it  is  liable 
to  spit,  exhibits  rootlets,  adheres  more  strongly  to  the  cupel,  and  is 
porous  towards  the  bottom.  The  buttons  are  then  weighed,  and, 
in  assays  of  top  and  bottom  samples,  either  the  average  percentage 
or  the  lowest  percentage  is  given.  The  loss  from  absorption  by 
the  cupel  (Kapellenzug)  is  added.1 

Bars  with  over  980  thousandths  of  silver  show  no  difference, 
if  the  work  has  been  carefully  done.  To  725  thousandths  they 
show  a  difference  of  J  to  3  thousandths;  from  720  to  710 
thousandths,  again,  no  difference,  or  only  an  infinitely  small  one 
(certain  chemical  combinations  seem  to  be  formed  at  this  per- 
centage); but  the  greatest  differences  occur  at  200  to  400 
thousandths  fineness.  Very  considerable  differences  may  occur  if 
the  bars  or  buttons  have  been  badly  fused.  The  silver  button 
contains  about  2  thousandths  of  lead. 

1  [The  quantity  of  silver  absorbed  by  the  cupel  is  very  small  and  need  only 
be  estimated  when  great  exactness  is  required.  The  white  portion  of  the 
cupel  is  broken  off  and  rejected ;  the  stained  portion  is  powdered  and  mixed 
with  charcoal  in  the  proportion  of  4  to  5  parts  by  weight  to  every  100  parts 
of  litharge  in  the  cupel,  together  with  from  100  to  250  grains  (G.5  to  1(J.2 
grammes)  of  a  mixture  of  equal  parts  fluor-spar,  borax,  and  carbonate  of  soda'. 
If  the  amount  of  litharge  in  the  cupel  is  small,  it  is  best  to  add  from  200  to 
300  grains  (13.0  to  19.5  grammes)  of  litharge  and  about  15  grains  (1  gramme) 
of  charcoal  to  the  mixture.  Should  the  silver  button  thus  obtained  be 
large,  the  cupel  used  in  this  case  should  be  examined  for  silver  in  a  similar 
manner,  and  even  a  third  or  fourth  cupel  may  be  similarly  treated. — G.] 


SILVER — ASSAYS   OF   ALLOYS. 


147 


Correction  Table  for  the  Absorption  by  the  Cupel,  determined  by 
the  French  Commission  on  Coinage  and  Medals. 


True  quantity  of 
silver. 

Loss  to  be  added, 
thousandths. 

True  quantity  of 
silver. 

Loss  to  be  added, 
thousandths. 

1000 

1.03 

500 

4.68 

975 

1.76 

475 

4.50 

950 

2.50 

450 

4.31 

925 

3.25 

425 

4.13 

900 

4.00 

400 

3.95 

875 

4.07 

375 

3.61 

850 

4.15 

350 

3.27 

825 

4.22 

325 

2.94 

800 

4.30 

300 

2.60 

775 

4.41 

275 

2.58 

750 

4.52 

250 

2.56 

725 

4  64 

225 

2.55 

700 

4.75 

200 

2.53 

675 

4.73 

175 

2.12 

650 

4.71 

150 

1.70 

625 

4.70 

125 

1.29 

600 

4.68 

100 

0.88 

575 

4.68 

75 

0.66 

550 

4.68 

50 

0.44 

525 

4.68 

25 

0.22 

In  Freiberg  somewhat  different  results  have  been  obtained. 
With  refined  silver  the  loss  by  absorption  by  the  cupel  was  found 
to  be  0.0015  to  0.002,  and  in  alloys  of  medium  richness  the  loss 
was  greater  than  that  stated  in  the  table;  for  instance,  with  750 
thousandths  and  16  weights  of  lead,  the  loss  was  5.55  thousandths, 
but  with  11  weights  of  lead  it  accorded  with  the  table,  4.52 
thousandths.  According  to  Plattner,  fine  silver  wdth  5  times  the 
quantity  of  lead  frequently  gives  a  loss  up  to  0.009,  refined  silver 
with  937  thousandths  and  5  times  the  quantity  of  lead,  0.0042 
to  0.0059;  refined  silver  with  687  to  750  thousandths  and  14 
times  the  quantity  of  lead,  0.0073  to  0.0083. 

B.  Wet  assays.1 

They  are  used  for  refined  silver  and  coin  alloys  of  copper  and 
silver.  Compared  with  the  fire  assay,  they  allow  of  an  accurate 
determination  of  the  degree  of  richness  to  within  0.5,  and  even 
to  0.1  thousandths.  They  are  more  frequently  volumetric  and 
gravimetric  assays. 


1  [Percy's  Metallurgy  of  Silver  and  Gold,  vol.  i.  p.  282.— G.] 


148  ASSAYING. 

1.  Volumetric  assays. 

a.  Gay-Lussac's  method  with  sodium  chloride.1 — This  method  is 
based  upon  the  precipitation  of  silver  from  a  nitric  acid  solution 
by  means  of  a  standard  solution  of  sodium  chloride.  For  this 
purpose  a  normal  solution  of  common  salt  is  required,  100  cubic 
centimeters  of  which  will  precipitate  1  gramme  of  chemically 
pure  silver.  There  is  further  required  a  decinormal  solution  of 
common  salt,  10  times  weaker  than  the  first,  and  a  decinormal 
solution  of  silver,  consisting  of  a  solution  of  silver  in  nitric  acid, 
containing  1  milligramme  of  silver  in  1  cubic  centimeter  of  solu- 
tion. 

Preparation  of  the  assay  solution. — The  degree  of  richness  of 
the  silver  is  approximately  determined  by  a  preliminary  assay, 
the  fine  assay  (p.  144)  being  generally  chosen  for  the  purpose. 
4  to  6  thousandths  parts  the  amount  of  silver  found  by  this 
assay  are  added  to  the  result.  It  is  generally  preferred  to 
assume  the  degree  of  richness  a  few  thousandths  higher  than  is 
actually  the  case,  and  to  base  the  calculation  for  the  quantity  of 
assay  sample  required  upon  this,  as,  to  effect  the  more  rapid 
settling  of  the  silver  chloride,  it  is  preferable  to  add,  during  the 
titration,  a  few  thousandths  from  the  decinormal  solution  of  salt 
than  to  be  obliged  to  add  from  the  decinormal  solution  of  silver. 
The  quantity  of  alloy  containing  1  gramme  of  silver  which  is  to 
be  taken  is  then  calculated  (for  instance,  if  the  preliminary  assay 
gives  a  percentage  of  897  thousandths,  then  1.115  grammes  of 
alloy  containing  1.000  gramme-  of  silver  should  be  taken, 
1000  :  897  =  x  :  1000).  The  sample  in  the  form  of  shavings 
or  granules  is  placed  in  a  numbered  flask,  together  with  6  to  7 
cubic  centimeters  of  nitric  acid  free  from  chlorine,  and  dissolved, 
either  on  a  water  or  sand  bath.  The  flasks  in  which  the  samples 
are  dissolved  are  from  10  to  15  centimeters  high,  and  5  to  5J 
centimeters  wide.  If  several  assays  are  to  be  made,  it  is  advisa- 
ble to  dip  the  flasks,  which  are  arranged  upon  a  stand  (Fig.  72), 

1  Gay-Lussac,  Vollst.  Unterricht  iiber  das  Verfahren,  Silber  auf  nassem 
Wege  zu  probiren,  Braunschweig,  1833 ;  Mulder,  Silberprobirmethode,  Leip- 
zig, 1859  ;  Muspratt's  Chem.,  Bd.  vi.  p.  477  ;  Bolley,  Handb.  der  techu.-chem. 
Untersuchung,  5  Aufl.  pp.  52,  332;  Dingier,  cxci.  172.  Trans.  Am.  Inst. 
Mining  Engineers,  vol.  iv.  p.  347;  vol.  x.  p.  493. 


SILVER — ASSAYS   OF   ALLOYS. 


149 


Fig.  72. 


into  hot  water.  (A  black  residue  may  be  gold  or  sulphide  of 
silver ;  should  the  latter  be  the  case,  some  concentrated  nitric 
acid  is  added  and  the  fluid  heated,  or  sulphuric 
acid  used.)  The  nitrous  acid  formed  is  then 
driven  out  of  the  flask  by  means  of  a  small 
bellows  with  curved  extremity,  and  the  con- 
tents of  the  flask  are  treated  with  the  normal 
solution.  But,  as  the  influence  of  the  tempera- 
ture upon  the  volume  of  the  normal  solution 
of  common  salt  must  be  taken  into  considera- 
tion, its  titer  must  always  be  determined  on  the  same  day  the 
assays  are  to  be  made,  with  1  gramme  of  pure  silver  -f  1  to  2 
cubic  centimeters  decinormal  solution  of  silver,  in  order  to  be 

Fig.  73. 


able,  for  the  above-mentioned  reason,  to  use  decinormal  solution 
of  salt  for  the  final  titration.  The  silver  solution  is  then  titrated 
by  placing  the  glass  flask  in  the  metal  cylinder  C  (Fig.  73) 


150 


ASSAYING. 


Fig.  74. 


standing  upon  the  sliding  carriage  B  (Sire's  apparatus1).  The 
glass  cock  c  (a  pinch-cock  may  be  used  instead)  is  then  opened, 
and,  accompanied  by  the  admission  of  air  through  a,  the  normal 
solution  of  sodium  chloride  flows  from  the  vessel  A  through  h, 
the  thermometer  tube  6,  and  the  rubber  tube  d,  into  the  burette  e. 
It  ascends  in  this,  and  a  small  quantity  reaches  the  saucer  g 
through  the  orifice  /.  The  cock  c  is  now  closed  (h  and  e  may  be 
also  directly  connected  by  a  rubber  tube  provided  with  a  clip), 
and  the  pipette  e,  which  is  now  filled,  will  contain  exactly  100 
cubic  centimeters  of  liquid.  The  index  finger  of  the  left  hand 
is  now  placed  upon  the  mouth  /  of  the  pipette,  the  rubber  tube  d 
is  detached  from  the  lower  end  of  the  pipette  e,  and  the  sliding 
carriage  B,  upon  which  stands  the  metal  cylinder  C  containing 

the  flask  with  the  solution  of  silver, 
is  pushed  underneath  the  discharge 
orifice  of  the  pipette.  The  index 
finger  is  now  removed  from  /,  and 
the  100  cubic  centimeters  of  the 
solution  of  common  salt  are  allowed 
to  run  into  the  flask,  care  being 
taken  that  the  pipette  does  not  rest 
on  the  neck  of  the  flask.  The  slid- 
ing carriage  is  then  pushed  back,  the 
flask  is  closed  with  its  ground-glass 
stopper,  and  its  contents  are  cleared 
by  shaking,  which  is  best  done  by 
inclosing  it  in  a  metal  cylinder  of 
proper  size  for  the  purpose.  If 
many  assays  are  to  be  made,  it  is 
advisable  to  use  Gay-Lussac's  or 
Mulder's  agitator. 

Gay-Lussac  '«  apparatus  (Fig.  74). 
—  Ay  a  stand  with  cylindrical  com- 
partments for  the  reception  of  the 
flasks  which  are  provided  with  well- 
ground  stoppers.  The  stand  is  sus- 
pended by  the  handle  e  f  to  the  steel  spring  e  d,  and  is  connected 


B.  u.  h.  Ztg.  1873,  p.  189. 


SILVER — ASSAYS   OF   ALLOYS.  151 

below  with  a  spiral  spring  a  b.      The  apparatus  is  shaken  by 
means  of  the  handle  e  f.1 

One  cubic  centimeter  of  decinormal  solution  is  now  added  to 
the  entirely  clear  fluid,  standing  over  the  precipitate  of  silver 
chloride,  by  means  of  a  graduated  pipette  contained  in  a  flask 
(Fig.  75),  whereby  the  point  of  the  pipette  should  be  placed 
against  the  neck  of  the  flask  containing  the  silver 
solution.     If  turbidity  is  produced,  the  silver  solu- 
tion is  agitated  until  it  is  again  clear,  and  1  cubic 
centimeter  of  the  decinormal  solution  of  common  salt 
again  added,  etc.,  until  the  last  cubic  centimeter  which 
is  added  does  not  produce  any  turbidity.     This  last 
cubic  centimeter  is  not  taken  into  calculation,  and 
only  one-half  of  the  one  previously  added.      (For  the  reason 
stated  on  p.  148,  it  is  more  suitable  to  use  decinormal  solution 
of  common  salt  than  decinormal  solution  of  silver  for  the  final 
reaction). 

Calculation. — Suppose  the  richness  of  the  alloy  was  found 
according  to  the  preliminary  assay  to  be  897  thousandths,  1115 
thousandths  of  the  sample  containing  1.000  gramme  would  have 
to  be  weighed  off.  1000  cubic  centimeters  of  the  decinormal 
solution  of  salt  =  1  gramme  of  silver.  Now  suppose  1002.5 
cubic  centimeters  of  decinormal  solution  of  common  salt  had 
been  used,  1000  parts  of  the  alloy  would  therefore  contain  899.1 
parts  of  silver. 

In  case  mercury2  should  be  present,  sodium  acetate  (0.5  gramme 
to  5  thousandths  of  mercury)  is  added,  which  will  prevent  the 
mercury  from  being  precipitated  by  the  sodium  chloride  solution  ; 
or  the  mercury  is  previously  volatilized  by  heating  the  sample  in 
a  small  graphite  crucible  in  the  muffle.  For  bismuth  some  tarta- 
ric  acid  is  added.  In  case  tin  is  present,  the  sample  is  dissolved 
in  sulphuric  acid  instead  of  nitric  acid.  According  to  Thorpe, 
only  2  parts  of  silver  chloride  freshly  precipitated,  and  0.8  part 
that  has  been  blackened  by  exposure  to  light,  are  dissolved  in 
100,000  parts  of  nitric  acid. 

[!  A  small  engine  is  sometimes  used  for  this  purpose.     Trans.  Am.  Inst. 
Mining  Engineers,  vol.  x.  p.  492. — Gr.] 
2  B.  u.  h.  Ztg.  1870,  p.  303. 


152  ASSAYING. 

Preparation  of  the  normal  solutions. — A  completely  saturated 
solution  of  common  salt  is  prepared,  of  which,  if  the  salt  used 
is  entirely  pure,  170  cubic  centimeters  contain  54.15  grammes 
of  common  salt.  These  170  cubic  centimeters  are  diluted  to  the 
volume  of  10  liters.  100  cubic  centimeters  of  this  solution 
correspond  to  0.5415  gramme  of  common  salt,  which  will  com- 
pletely precipitate  1  gramme  of  pure  silver.  The  true  standard 
is  obtained  by  pouring  100  cubic  centimeters  of  the  solution  of 
common  salt  into  a  solution  of  1  gramme  of  chemically  pure 
silver.  This  is  agitated  by  shaking  until  it  becomes  clear,  and 
the  number  of  thousandths  of  common  salt  or  silver  which  re- 
main free  are  exactly  determined  by  the  addition  of  an  observed 
volume  of  very  dilute  salt  solution  of  known  strength,  or  of  a 
decinormal  solution  of  silver,  and  from  this  the  quantity  of 
water  or  of  common  salt  is  calculated  which  must  be  added  to 
obtain  the  correct  standard.  When  this  addition  has  been  made, 
a  new  test  is  had  with  the  standard  solution  and  the  decinor- 
mal solution  prepared  from  it,  and  this  is  continued  until  the 
solution  does  not  show  a  perceptible  variation  from  the  correct 
standard.  The  decinormal  solution  of  common  salt  is  prepared 
by  pouring  100  cubic  centimeters  of  the  standard  solution  of 
salt  into  a  flask  capable  of  holding  1  liter  and  filling  it  with 
water  to  the  liter  mark.  For  the  decinormal  solution  of  silver, 
1  gramme  of  fine  silver  is  dissolved  in  5  to  6  grammes  of  nitric 
acid,  which  is  then  diluted  with  water  to  1  liter. 

When  a  large  number  and  great  variety  of  silver  alloys  have  to 
be  assayed,  the  following  tables,  A  and  B,  calculated  by  Gray-Lussac 
for  his  silver  assay,  will  be  found  to  save  much  time  and  trouble  in 
determining  the  fineness  of  the  alloy.  If,  after  the  addition  of  the 
standard  (common)  salt  solution,  no  reaction  takes  place  on  adding 
the  decimal  salt  solution  or  the  decimal  silver  solution,  it  is  an  indi- 
cation that  the  silver  in  the  alloy  assayed  amounts  to  exactly  1000 
milligrammes,  and  it  further  indicates  that  the  standard  solution  is 
correct.  This  titer  is  indicated  in  the  columns  by  the  figure  O.1 

i  Portschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  101. 


SILVER — ASSAYS   OF  ALLOYS. 
Table  A. — For  decimal  salt  solution. 


153 


°  is§ 

*o*si 

^S.2* 

Cubic  centimeters  of  decinormal  salt  solution  added. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

correspond  to  a  content  of  fine  silver  of 

1000 

1000.01    — 

— 

— 

— 

— 

— 

— 

— 





1003 

997.0 

998.0 

999.0 

1000.0 









__ 

_^ 

1005 

995.0 

996.0997.0 

998.0999.0 

1000.0 







__ 

__ 

1007 

993.0 

994.0 

995.0 

996.0997.0 

998.0999.0 

1000.0 



__ 

__ 

1009 

991.0 

992.0 

993.0 

994.0  995.0 

996.0997.0 

998.0 

999.0 

1000.0 



1010 

990.1 

991.1 

992.1 

993.1  994.1 

995.0996.0 

997.0 

998.0 

999.0 

1000.0 

1011 

989.1 

990.1 

991.1 

992.1J993.1 

994.1  995.1 

996.0 

997.0 

998.0 

999.0 

1015 

985.2 

986.2 

987.2 

988.2 

989.2 

990.1  991.1 

992.1 

993.1 

994.1 

995.1 

1020 

980.4 

981.4 

982.4 

983.3 

984.3 

985.3!986.3 

987.2 

988.2 

989.2 

990.2 

1025 

975.6 

976.6 

977.6 

978.5 

979.5 

980.5  981.5 

982.4 

983.4 

984.4 

985.4 

1030 

970.9 

971.8 

972.8 

973.8 

974.8 

975.7976.7 

977.7 

978.6 

979.6 

980.6 

1035 

966.2 

967.1 

968.1 

969.1 

970.0 

971.0972.0 

972.9 

973.9 

974.9 

975.8 

1040 

961.5 

962.5 

963.5 

964.4965.4 

966.3967.3 

968.3 

969.2 

970.2 

971.1 

1045 

956.9 

957.9 

958.8 

959.8960.8 

961.7 

962.7 

963.6 

964.6 

965.5 

966.5 

1050 

952.4 

953.3 

954.3 

955.2 

956.2 

957.1 

958.1 

959.0 

960.0 

960.9 

961.9 

1055 

947.9 

948.8 

949.8 

950.7 

951. 

952.6 

953.5 

954.5 

955.4 

956.4 

957.3 

1060 

943.4 

944.3 

945.3 

946.2 

947. 

948.1 

949.1 

950.0 

950.9 

951.9 

952.8 

1065 

939.0 

939.9 

940.8 

941.8 

942. 

943.7 

944.6 

945.5 

946.5 

947.4 

948.4 

1070 

934.6 

935.5 

936.4 

937.4 

938. 

939.3 

940.2 

941.1 

942.1 

943.0 

943.9 

1075 

930.2 

931.2 

932.1 

933.0 

933. 

934.9 

935.8 

936.7 

937.7 

938.6 

939.5 

1080 

925.9 

926.8 

927.8 

928.7 

929. 

930.6(931. 

932.4 

933.3 

934.3 

935.2 

1085 

921.7 

922.6 

923.5 

924.4 

925. 

926.3 

927. 

928.1 

929.0 

930.0 

930.9 

1090 

917.4 

918.3 

919.3 

920.2 

921. 

922.0 

922. 

923.8 

924.8 

925.7 

926.6 

1095 

913.2 

914.2 

915.1 

916.0 

917. 

917.8 

918. 

919.6 

920.5 

921.5 

922.4 

1100 

909.1 

910.0 

910.9 

911.8 

912. 

913.6 

914. 

915.4 

916.4 

917.3 

918.2 

1105 

905.0 

905.9 

906.8 

907.7 

908. 

909.5 

910. 

911.3 

912.2 

913.1 

914.0 

1110 

900.9 

901.8 

902.7 

903.6 

904. 

905.4 

906. 

907.2 

908.1 

909.0 

909.9 

1115 

896.9 

897.8 

898.6 

899.5 

900.4 

901.3 

902. 

903.1 

904.0 

904.9 

905.8 

1120 

892.9 

893.7 

894.6 

895.5 

896.4 

897.3 

898. 

899.1 

900.0 

900.9 

901.8 

1125 

888.9 

889.8 

890.7 

891.6 

892.4 

893.3 

894. 

895.1 

896.0 

896.9 

897.8 

1130 

885.0 

885.8 

886.7 

887.6 

888.5 

889.4 

890. 

891.2 

892.0 

892.9 

893.8 

1135 

881.1 

881.9 

882.8 

883.7 

884.6 

885.5 

886. 

887.2 

888.1 

889.0 

889.9 

1140 
1145 

877.2 
873.4 

878.1 

874.2 

878.9 
875.1 

879.8 
876.0 

880.7 
876.9 

881.6 

877.7 

882. 
878.6 

883.3 
879.5 

884.2 
880.3 

885.1 

881.2 

886.0 
882.1 

1150 

869.6870.4 

871.3 

872.2 

873.0 

873.9 

874.8 

875.7 

876.5 

877.4 

878.3 

1155 

865.8 

866.7 

867.5 

868.4 

869.3 

870.1 

871.0 

871.9 

872.7 

873.6 

874.5 

1160 

862.1 

862.9 

863.8 

864.7 

865.5 

866.4 

867.2 

868.1 

869.0 

869.8 

870.7 

1165 

858.4 

859.2 

860.1 

860.9 

861.8 

862.7 

863.5 

864.4 

865.2 

866.1 

866.9 

1170 

854.7 

855.6 

856.4 

857.3 

858.1 

859.0 

859.8 

860.7 

861.5 

862.4 

863.2 

1175 

851.1 

851.9 

852.8 

853.6 

854.5 

855.3 

856.2 

857.0 

857.9 

858.7 

859.6 

1180 

847.5 

848.3 

849.2 

850.0 

850.8 

851.7 

852.5 

853.4 

854.2 

855.1 

855.9 

1185 

843.9 

844.7 

845.6 

846.4 

847.3 

848.1 

848.9 

849.8 

350.6 

851.5 

852.3 

1190 

840.3 

841.2 

842.0 

842.9 

843.7 

844.5 

845.4 

846.2 

847.1 

847.9 

848.7 

1195 

836.8 

S37.7 

838.5 

839.3 

840.2 

841.0 

841.8 

842.7 

843.5 

844.3 

845.2 

1200 

833.3 

834.2 

835.0 

835.8 

836.7 

837.5 

838.3 

839.2 

840.0 

840.8 

841.7 

1205 

829.9 

830.7 

831.5 

832.4 

833.2 

834.0 

834.8 

835.7 

836  5 

837.3 

838.2 

1210 

826.4 

827.3 

828.1 

828.9 

829.7 

830.6 

831.4 

832.2 

833.1 

833.9 

834.7 

1215 

823.0 

823.9 

824.7 

825.5 

826.3 

827.2 

828.0 

828.8 

829.6 

830.4 

831.3 

1220 

819.7 

820.5 

821.3 

822.1 

822.9 

823.8 

824.6 

825.4 

826.2 

827.0 

827.9 

1225 

816.3 

817.1 

818.0 

818.8 

819*6 

820.4 

821.2 

822.0 

822.9 

823.7 

824.5 

1230 

813.0 

813.8 

814.6 

815.4 

816.3 

817.1 

817.9 

818.7 

819.5 

820.3 

821.1 

1235 

809.7 

810.5 

811.3 

812.1 

813.0 

813.8 

814.6 

815.4 

816.2 

817.0 

817.8 

1240 

806.5 

807.3 

808.1 

808.9 

809.7 

810.5 

811.3 

812.1 

812.9 

813.7 

814.5 

1245 

803.2 

804.0 

804.8 

805.6 

806.4 

807.2 

808.0 

808.8 

809.6 

810.4 

811.2 

1250 

800.0 

809.8 

801.6 

802.4 

803.2 

804.0 

804.8 

805.6 

806.4 

807.2 

808.0 

1255 

796.8 

797.6 

798.4 

799.2 

800.0 

800.8 

801.6 

802.4 

803.2 

804.0 

804.8 

154 


ASSAYING. 

Table  B. — For  decinormal  silver  solution. 


<«-.               »-     .     3D 

z  •§-§ 
S^fis 

j^ssa 

Cubic  centimeters  of  decinormal  silver  solution  added. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

correspond  to  a  content  of  fine  silver  of 

1000 

1000.0 

999.0 

998.0 

997.0 

996.0 

995.0 

994.0 

993.0 

992.0(991.0 

990.0 

1003 

997.0 

996.0 

995.0 

994.0 

993.0 

992.0 

1)91.0 

990.0 

989.0 

988.0 

987.0 

1005 

995.0 

994.0 

993.0 

992.0 

991.0 

990.0 

989.0 

988.1 

987.1 

986.1 

985.1 

1007 

993.0 

992.0 

991.1 

990.1 

989.1 

988  1 

987.1 

986.1 

985.1 

984.1 

983.1 

1009 

991.0 

990.0 

989.0 

988.0 

987.0 

986.0 

985.0 

984.0 

983.0 

982.0 

981.0 

1010 

990.1 

989.1 

988.1 

987.1 

986.1 

985.1 

984.2 

983.2 

982.2 

981.2 

980.2 

1011 

989.1 

988.1 

987.1 

986.2 

985.2 

984.2 

983.2 

982.2 

981.2 

980.2 

979.2 

1015 

985.2 

984.2 

983.2 

982.3 

981.3 

980.3 

979.3 

978.3 

977.3 

976.4 

975.4 

1020 

980.4 

979.4 

978.4 

977.4 

976.5 

975.5 

974.5 

973.5 

972.5 

971.6 

970.6 

1025 

975.6 

974.6 

973.7 

972.7 

971.7 

970.7 

969.8 

968.8 

967.8 

966.8 

965.8 

1030 

970.9 

969.9 

968.9 

968.0 

967.0 

966.0 

965.0 

964.1 

963.1 

962.1 

961.2 

1035 

966.2 

965.2 

964.2 

963.3 

962.3 

961.3 

960.4 

959.4 

958.4 

957.5 

956.5 

1040 

961.5 

960.6 

959.6 

958.6 

957.7 

956.7 

955.8 

954.8 

953.8 

952.9 

951.9 

1045 

956.9 

956.0 

955.0 

954.1 

953.1 

952.1 

951.2 

950.2 

949.3 

948.3 

947.4 

1050 

952.4 

951.4 

950.5 

949.5 

948.6 

947.6 

946.7 

945.7 

944.8 

943.8 

942.9 

1055 

947.9 

946.9 

946.0 

945.0 

944.1 

943.1 

942.2 

941.2 

940.3 

939.3 

938.4 

1060 

943.4 

9424 

941.5 

940.6 

939.6 

938.7 

937.7 

936.8 

935.8 

934.9 

934.0 

1065 

939.0 

938.0 

937.1 

936.1 

935.2 

934.3 

933.3 

932.4 

931.4 

930.5 

929.6 

1070 

934.6 

933.6 

932.7 

931.8 

930.8 

929.9 

929.0 

928.0 

927.1 

926.2 

925.2 

1075 

930.2 

929.3 

928.4 

927.4 

926.5 

925.6 

924.7 

923.7 

922.8 

921.9 

920.9 

1080 

925.9 

925.0 

924.1 

923.1 

922.2 

921.3 

920.4 

919.4 

918.5 

917.6 

916.7 

1085 

921.7 

920.7 

919.8 

918.9 

918.0 

917.0 

916.1 

915.2 

914.3 

913.4 

912.4 

1090 

917.4 

916.5 

915.6 

914.7 

913.8 

912.8 

911.9 

911.0 

910.1 

909.2 

908.3 

1095 

913.2 

912.3 

911.4 

910.5 

909.6 

908.7 

907.8 

906.8 

905.9 

905.0 

904.1 

1100 

909.1 

908.2 

907.3 

906.4 

905.4 

904.5 

903.6 

902.7 

901.8 

900.9 

900.0 

1105 

905.0 

904.1 

903.2 

902.3 

901.4 

900.4 

899.5 

898.6 

897.7 

896.8 

895.9 

1110 

900.9 

900.0 

899.1 

898.2 

897.3 

896.4 

895.5 

894.6 

893.7 

892.8 

891.9 

1115 

896.9 

896.0 

895.1 

894.2 

893.3 

892.4 

891.5 

890.6 

889.7 

888.8 

887.9 

1120 

892.9 

892.0 

891.1 

890.2 

889.3 

888.4 

887.5 

886.6 

885.7 

884.8 

885.9 

1125 

888.9 

888.0 

887.1 

886.2 

885.3 

884.4 

883.6 

882.7 

881.8 

880.9 

880.0 

1130 

885.0 

884.1 

883.2 

882.3 

881.4 

880.5 

879.6 

878.8 

877.9 

877.0 

876.1 

1135 

881.1 

880.2 

879.3 

878.4 

877.5 

876.7 

875.8 

874.9 

874.0 

873.1 

872.3 

1140 

877.2 

876.3 

875.4 

874.6 

873.7 

872.8 

871.9 

871.0 

870.2 

869.3 

868.4 

1145 

873.4 

872.5 

871.6 

870.7 

869.9 

869.0 

868.1 

867.2 

866.4 

865.5 

864.6 

1150 

869.6 

868.7 

867.8 

867.0 

866.1 

865.2 

864.3 

863.5 

862.6 

861.7 

860.9 

1155 

865.8 

864.9 

864.1 

863.2 

862.3 

861.5 

860.6 

859.7 

858.9 

858.0 

857.1 

1160 

862.1 

861.2 

860.3 

859.5 

858.6 

857.8 

856.9 

856.0 

855.2 

854.3 

853.4 

1165 

858.4 

857.5 

856.6 

855.8 

854.9 

854.1 

853.2 

852.4 

851.5 

850.6 

849.8 

1170 

854.7 

853.8 

853.0 

852.1 

851.3 

850.4 

849.6 

848.7 

847.9 

847.0 

846.1 

1175 

851.1 

850.2 

849.4 

848.5 

847.7 

846.8 

846.0 

845.1 

844.3 

843.4 

842.5 

1180 

847.5 

846.6 

845.8 

844.9 

844.1 

843.2 

842.4 

841.5 

840.7 

839.8 

839.0 

1185 

843.9 

843.0 

842.2 

841.3 

840.5 

839.7 

838.8 

838.0 

837.1 

836.3 

835.4 

1190 

840.3 

839.5 

838.7 

837.8 

837.0 

836.1 

835.3 

834.5 

833.6 

832.8 

831.9 

1195 

836.8 

836.0 

835.1 

834.3 

833.5 

832.6 

831.8 

831.0 

830.1 

829.3 

828.4 

1200 

833.3 

832.5 

831.7 

830.8 

830.0 

829.2 

828.3 

827.5 

826.7 

825.8 

825.0 

1205 

829.9 

829.0 

828.2 

827.4 

826.6 

825.7 

824.9 

824.1 

823.2 

822.4 

821.6 

1210 

826.4 

825.6 

824.8 

824.0 

823.1 

822.3 

821.5 

820.7 

819.8 

819.0 

818.2 

1215 

823.0 

822.2 

821.4 

820.6 

819.7 

818.9 

818.1 

817.3 

816.5 

815.6 

814.8 

1220 

819.7 

818.8 

818.0 

817.2 

816.4 

815.6 

814.7 

813.9 

813.1 

812.3 

811.5 

1225 

816.3 

815.5 

814.7 

813.9 

813.1 

'812.2 

811.4 

810.6 

809.8 

809.0 

808.2 

1230 

813.0 

812.2 

811.4 

810.6 

809.8 

808.9 

808.1 

807.3 

806.5 

805.7 

804.9 

1235 

809.7 

808.9 

808.1 

807.3 

806.5 

805.7 

804.9 

804.0 

803.2 

802.4 

801.6 

1240 

806.5 

805.6 

804.8 

804.0 

803.2 

802.4 

801.6 

800.8 

800.0 

799.2 

798.4 

1245 

803.2 

802.4 

801.6 

800.8 

800.0 

799.2 

798.4 

797.6 

796.8 

796.0 

795.2 

1250 

800.0 

799.2 

798.4 

797.6 

796.8 

796.0 

795.2 

794.4 

793.6 

792.8 

792.0 

1255 

796.8 

796.0 

795.2 

794.4 

793.6 

792.8 

792.0 

791.2 

791.4 

789.6 

788.8. 

SILVER — ASSAYS  OF  ALLOYS.  155 

In  making  Gay-Lussac's  assay  of  silver  bullion  a  great  deal  of 
time  is  necessarily  spent  in  waiting  for  the  suspended  chloride  to 
settle  and  leave  the  liquid  clear  in  order  to  observe  the  action  of  the 
next  drop  of  the  precipitant.  Whittell1  has  reduced  this  loss  of 
time  and  insured  greater  facility  in  making  the  assay  by  dividing 
the  solution  (containing  the  silver)  into  several,  say  five,  equal 
parts  in  separate  vessels.  They  are  placed  in  a  row,  and  3  c.c.  of 
salt  solution  added  to  the  first,  4  c.c.  to  the  second,  5  c.c.  to  the 
next,  and  so  on.  After  the  precipitate  has  subsided,  -J  c.c.  of  the 
same  solution  is  added  to  each  successively.  Numbers  1,  2,  and  3 
will  perhaps  show  traces  of  silver  still  in  solution,  but  numbers  4 
and  5  none.  The  amount  precipitated  from  number  3  multiplied 
by  5  (as  it  represents  only  \  of  the  original  solution  of  silver)  will 
be  the  amount  of  silver  contained  in  the  ore  or  alloy  being  assaved. 
A  simple  means  of  settling  the  precipitated  chloride  almost  instan- 
taneously is  to  agitate  the  solution  with  a  few  drops  of  chloroform. 
Its  action  seems  to  be  entirely  mechanical.  The  agitation  displaces 
the  chloroform  in  minute  globules  throughout  the  silver  solution, 
which  in  settling  to  the  bottom  carries  with  it  every  particle  of  the 
chloride. 

b.  Volhard's  assay  with  sulpho-cyanide.2 — The  solution  of  sil- 
ver, which  should  be  free  from  nitrous  acid,  mercury,  and  palla- 
dium, and  to  which  has  been  added  some  ferric  sulphate,  is 
precipitated  in  the  cold  with  titrated  potassium  sulpho-cyanide 
until  a  permanent  red  coloration  from  iron  remains,  indicating 
that  all  the  silver  has  been  precipitated.  The  assay,  which  is  as 
accurate  as  Gay-Lussac's,  is  simpler,  and  can  be  executed  more 
quickly,  and  allows  at  the  same  time  of  a  determination  of  a  per- 
centage of  gold  in  the  same  assay  sample. 

The  standard  solution  of  potassium  sulpho-cyanide  is  prepared 
by  dissolving  10  grammes  of  chemically  pure  silver  in  nitric 
acid  free  from  chlorine,  and  diluting  it  to  1  liter ;  50  cubic  centi- 
meters of  this  solution  are  placed  in  a  beaker-glass  and  diluted 
with  3  to  4  times  its  volume  of  water ;  5  cubic  centimeters  of  a 

1  Humid  Assay  for  Silver.     Dr.  A.  P.  Whittell,  Engineering  and  Mining 
Journal,  Nov.  26,  1881,  p.  356. 

2  Volhard,  die   Silbertitrirung  mit  Sohwefelcyanammonium,  etc.,  Leipzig, 
Winter,  1878;  Dingier,  ccxiv.  399  ;  B.  u.  h.  Ztg.  1875,  p.  83;  1876,  p.  405  • 
(Lindeman)  ;  Fresenius's  Ztschr.  xiii.  171 ;  1878,  p.  482. 


156  ASSAYING. 

pure  solution  of  ferric  sulphate  (1  part  of  the  salt  in  10  parts  of 
water)  are  added  to  it,  and  the  solution  of  potassium  sulpho- 
cyanide  is  allowed  to  flow  to  it,  under  constant  stirring,  from  a 
burette  holding,  50  cubic  centimeters  and  divided  into  y1^  and 
filled  exactly  to  the  0  point,  until  the  color  of  the  solution  re- 
mains permanently  red.  The  assay  fluid  is  prepared  by  placing 
10  grammes  of  the  silver  in  a  long-necked  flask,  capable  of  hold- 
ing from  200  to  250  cubic  centimeters.  It  is  then  dissolved  on 
the  sand-bath  in  50  cubic  centimeters  of  nitric  acid  free  from 
chlorine,  of  1.2  specific  gravity,  and  diluted  with  distilled  water. 
Any  gold  which  may  be  present  is  then  allowed  to  settle,  and 
the  clear  silver  solution  is  poured  into  a  flask  capable  of  holding 
1  liter.  The  residuum  is  several  times  digested  with  a  small 
quantity  of  nitric  acid,  and  is  then  decanted  with  distilled  water 
until  the  liter  flask  is  nearly  full  to  the  liter  mark,  and  the 
wash-water  shows  no  traces  of  silver.  The  flask  in  which  the 
solution  was  made  is  now  filled  to  the  rim  with  water  and  in- 
verted in  a  porcelain  crucible,  to  remove  the  gold  contained  in  it, 
and  the  gold,  which  is  weighed  to  within  0.0002  gramme,  is 
further  treated  according  to  the  assay  method,  which  will  be 
given  further  on.  The  solution  of  silver  in  the  liter  flask  is 
now  diluted  to  1  liter,  50  cubic  centimeters  of  it  are  measured 
out  in  a  beaker-glass,  and  titrated  with  the  solution  of  potassium 
sulpho-cyanide,  after  addition  of  ferric  sulphate. 

Cobalt  and  nickel  produce  peculiar  tints  which  can  be  easily 
distinguished  from  those  of  the  reaction  of  the  silver.  In  case 
the  sample  contains  more  than  80  per  cent,  of  copper,  the  red 
coloring  is  not  very  perceptible,  and  Volhard  and  Fresenius1 
have  given  a  modification  for  this  emergency;  or  pure  silver 
may  be  added  to  the  sample.  Mercury  is  removed  by  previous 
volatilization,  and  nitrous  acid  must  be  completely  removed  by 
boiling,  as  it  decomposes  sulpho-cyanic  acid,  even  in  the  cold, 
while  nitric  acid  will  only  do  so  when  heated.  A  small  percent- 
age of  chlorine  in  the  solution  of  potassium  sulpho-cyanide  does 
not  cause  any  trouble,  but  a  large  amount  of  it  is  injurious. 

1  Fresenius's  Ztschr.  xiii.  175. 


SILVEE — ASSAYS  OF  ALLOYS.  157 

c.  Determination  of  silver  and  copper  in  one  solution. — Ques- 
sand's1  method  of  determining  both  these  metals  in  one  solution  is 
based  upon  the  fact  that  in  the  simultaneous  presence  of  copper  and 
silver  only  the  latter  is  at  first  precipitated  by  potassium  ferro- 
cyanide;  the  pure  white  precipitate  of  ferrocyanide  of  silver  assumes 
a  pale  flesh  color  only  when  the  copper  begins  to  separate  out,  which 
cannot  begin  until  all  the  silver  has  been  precipitated.     The  pre- 
cipitation of  the  copper  is  finished  when  the  supernatant  liquid  has 
acquired  a  reddish  color,  which  is  due  to  a  trace  of  the  cupric  ferro- 
cyanide being  soluble  in  potassium  ferrocyanide.     The  assay  must 
be  made  by  a  neutral  or  only  slightly  acid  one  per  cent,  solution  of 
potassium  ferrocyanide.     For  settling  the  titer  a  solution  is  used  of 
one  gramme  of  pure  silver  and  0.1  gramme  of  pure  copper  in  3  c.c. 
of  HN03,  diluted  with  water  to  400  c.c.,  and  a  solution  of  one 
gramme  of  Rochelle  salt  (sodium  tartrate)  and  25  c.c.  of  caustic 
soda  in  500  c.c.  of  water.     The  latter  solution  serves  as  an  addi- 
tional proof  of  the  precipitation  of  the  copper,  the  reddish  color  of 
the  supernatant  liquid  being  changed  to  bluish-white  by  its  addition. 

d.  Assay  by  iodide  of  potassium  and  starch."1 — On  adding  HN03, 
nitrous  acid,  iodide  of  potassium,  and  starch  to  a  solution  contain- 
ing a  silver  salt,  two  reactions  take  place.     Iodide  of  silver  is  pre- 
cipitated ;  and  iodide  of  starch  is  produced,  which  colors  the  liquid 
blue.     So  long  as  the  least  excess  of  silver  remains  undecomposed 
this  coloration  disappears  at  once  on  shaking ;  but  if  by  a  fresh 
addition  of  iodide  of  potassium  the  point  of  saturation  has  been 
reached,  a  single  drop  of  the  reagent  suffices  to  give  a  permanent 
blue  color  to  the  entire  solution.     The  necessary  solutions  are  thus 
prepared:    Ten  grammes  of  commercial  iodide  of  potassium  are 
dissolved  in  distilled  water,  so  that  the  volume  is  1023.4  c.c.     One 
cubic  centimeter  of  this  solution  will  precipitate  0.01  gramme  of 
silver.     The  HN03,  containing  nitrous  acid,  is  prepared  by  adding 
1  gramme  of  pure  sulphate  of  protoxide  of  iron  to  1000  grammes 
of  HN03,  of  sp.  gr.  1.200;   and  a  small  quantity  of  the  iron  salt 
must  be  added  from  time  to  time.     The  starch  is  prepared  by  treat- 
ing one  part  of  starch  with  100  parts  warm  water,  the  solution 
allowed  to  settle,  and  the  clear  liquid  decanted ;  to  this,  20  parts  of 
pure  nitrate  of  potash  are  added. 

1  Chemikerztg.,  1884,  p.  1655. 

2  Annales  des  Mines,  1856,  vol.  10,  p.  83  ;  Chem.  News,  1860,  vol.  2,  p.  17; 
Fogg.  Ann.,  1865,  124,  p.  347. 


158  ASSAYING. 

In  making  an  assay  by  this  method,  1  c.c.  of  the  HN03  is  added 
to  1  c.c.  of  the  solution  under  examination,  then  10  or  12  drops  of 
starch  solution,  and  a  few  drops  of  iodide  of  potassium.  The  addi- 
tion of  the  iodide  is  .carefully  continued  until  a  permanent  blue 
coloration  is  produced,  and  the  number  of  c.c.  added  gives  a  direct 
measure  to  the  number  of  centigrammes  present.  This  method 
yields  excellent  results  in  presence  of  acids  and  organic  bodies,  but 
is  not  applicable  in  presence  of  salts  of  mercury,  protoxide  of  tin, 
arsenious  acid,  etc.,  which  decompose  iodide  of  starch,  or  substances 
which  color  the  solution. 

2.  Gravimetric  analysis. — As  the  solution  of  common  salt 
evaporates  too  much  in  a  hot  climate,  the  following  method  is 
used  in  the  East  Indies:1  1.22  grammes  of  the  alloy  are  dis- 
solved in  nitric  acid.  The  silver  is  precipitated  by  hydrochloric 
acid,  and  the  silver  chloride  is  carefully  washed  out.2  The  flask 
is  filled  with  water  and  inverted  in  a  smooth  washing  crucible, 
and  then  removed.  The  greatest  part  of  the  water  is  decanted 
off,  and  the  assay  dried,  first  on  the  water-bath,  and  next  in  an 
air-bath  at  150°  to  170°  C.  (302°  to  338°  F.),  and  the  silver 
chloride  weighed  while  still  warm. 

Determination  of  selenium  in  silver.9 — Silver  used  for  parting 
alone  contains  selenium  ;  it  is  never  found  in  fine  silver.  Its  pres- 
ence originates  from  the  H,S04  used  in  parting;  this  acid  is  mostly 
produced  from  pyrites,  which  usually  contains  selenium.  In  pre- 
cipitating the  silver  from  the  H2S04  solution  with  copper,  the  entire 
content  of  selenium  is  also  precipitated.  If  the  solution  contains 
no  more  than  .001  per  cent,  of  selenium,  the  silver  becomes  brittle, 
and  the  surface  of  the  metal  is  covered  with  gray  stains  of  selenide 
of  silver  which,  being  distributed  throughout  the  entire  mass,  can- 
not be  removed  by  polishing.  In  melting  such  silver  with  copper 
a  vigorous  boiling  takes  place  and  particles  of  the  alloy  are  apt  to 
be  thrown  out  and  lost.  This  is  caused  by  the  formation  of  seleni- 
ous  acid,  which  is  formed  by  the  action  of  the  oxygen,  present  in  the 
copper  as  protoxide,  upon  the  selenium  and  escaping  as  a  gas. 

1  Dingier,  cciii.  97,  203. 

2  [This  operation  should  be  very  carefully  repeated  until  the  precipitate  is 
thoroughly  washed.     Instead  of   decanting  the  supernatant  liquid  can  be 
siphoned  off. — Gr.] 

3  Fortschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  107. 


SILVER — ASSAYS   OF   ALLOYS. 


The  method  of  determining  selenium  in  silver  is,  according  to 
Debray,  as  follows:  Dissolve  100  grammes  of  the  silver  in  HNOS  of 
34  °B.  (1.3  sp.gr.),  decant  the  silver  solution  from  any  gold  which  may 
be  present,  precipitate  the  silver  with  HC1,  filter  and  dry  filtrate  on 
a  water-bath.  Then  boil  with  a  few  drops  of  HC1  in  order  to  con- 
vert the  selenic  acid  into  selenious  acid,  and  then  add  sulphurous 
acid,  or,  with  an  excess  of  acid,  sodium  sulphite,  whereby  the  sele- 
nious acid  is  reduced.  Boil  for  one  hour  until  the  precipitate  of 
selenium,  at  first  red,  becomes  black,  collect  upon  a  weighed  filter, 
dry  at  a  temperature  of  not  over  100°  C.  (212°  F.)  and  weigh. 
The  filtrate  from  this  precipitate  of  selenium  is  evaporated  and 
again  treated  in  the  same  manner  in  order  that  the  precipitation  of 
the  selenium  may  be  complete. 

Selenated  silver  can  also  be  readily  freed  from  its  selenium  by 
remelting  with  saltpetre. 

3.  Electrolytic  determination  of  silver. — Luckow1  as  early  as  1865 
gave  a  method  for  the  quantitative  determination  of  silver  by  elec- 
trolysis.    According  to  his  later  communications,2  precipitation  of 
the  silver  is  completely  effected   by  passing  the  galvanic  current 
through  a  solution  containing  at  the  most  8  to  10  per  cent,  of  free 
HNOa.    The  silver  is  then  precipitated  in  a  very  voluminous  spongy 
condition.    Some  binoxide  is  simultaneously  formed  on  the  positive 
pole;  its  formation,  however,  can  be  prevented  by  .the  addition  of 
glycerin,  milk-sugar,  or  tartaric  acid.    The  precipitation  of  the  silver 
in  this  spongy,  flaky  form  is  very  inconvenient,  as  it  easily  drops 
from,  the  electrode  and  cannot  be  readily  weighed.     Such  metallic 
sponge  is  more  especially  obtained  from  comparatively  concentrated 
solutions.    According  to  H.  Fresenius  and  F.  Bergmann,3  the  silver 
can  be  precipitated  from  HN03  solutions  in  a  compact  and  beautiful 
form,  provided   the  solution  be  diluted  and  the  galvanic  current 
weak.     It  is  suggested  that  200  c.c.  of  the  liquid  to  be  electrolyzed 
contains  not  more  than  0.03  to  0.04  gramme  of  metallic  silver  and 
not  over  3  to  6  grammes  of  free  HN03,  that  the  electrodes  be  not 
over  one  centimeter  apart,  and  that   the  strength  of  the  current 
equals  about  100  to  150  c.c.  of  oxyhydrogen  gas  per  hour.     From 
neutral  or  slightly  acid  solutions  there  is  precipitated,  according  to 

1  Dingler's  Journ.  Bd.  178,  p.  43. 

2  Ztschft.  f.  Anal.  Chem.  Bd.  19,  p.  15. 

3  Ztschft.  f.  Anal.  Chem.  Bd.  19,  p.  324. 


160  ASSAYING. 

Kiliani,1  besides  metallic  silver  on  the  cathode,  silver  dioxide  on 
the  anode  ;  the  amount  of  the  latter  varies  according  to  the  acidity 
and  the  amount  of  silver  in  the  solution.  To  prevent  the  formation 
of  this  dioxide  Kiliani  adds  lead  nitrate  to  the  solution,  the  quan- 
tity thus  added  being  greater  than  the  amount  of  silver.  Under 
these  circumstances  only  lead  dioxide  separates  upon  the  anode, 
which  exerts  no  influence  upon  the  separation  of  the  silver  in  the 
cathode. 

Schucht2  states  that  from  all  solutions  except  nitrates,  or  such  as 
contain  much  free  HNO3,  nothing  but  the  metallic  silver  is  pre- 
cipitated, and  that  the  greatest  amount  of  silver  dioxide  is  precipi- 
tated from  concentrated  acid  solutions. 

According  to  Classen,  an  excess  of  ammonium  oxalate  is  added  to 
the  silver  solution,  the  white  precipitate  thoroughly  washed  and 
dissolved  in  a  solution  of  potassium  cyanide.  The  current  should 
not  exceed  80  to  100  c.c  of  oxyhydrogen  gas  per  hour  ;  one  Bunsen 
cell  will  therefore  be  found  sufficient.  If  the  silver  is  to  be  sepa- 
rated from  copper,  the  latter  can  be  readily  determined  in  the  solu- 
tion after  the  precipitated  silver  has  been  filtered  off.  To  analyze 
an  alloy  of  copper  and  silver  dissolve  about  0.1  gramme  in  HN03, 
evaporate  to  dryness,  take  up  with  water  and  add  ammonium 
oxalate  until  the  precipitate  appears  pure  white.  Dissolve  in 
potassium  cyanide  and  proceed  as  above. 

C.  Hydrostatic- assay. — According  to  Karmarsch* the  quantity 
of  silver  in  coins  can  be  determined  from  the  specific  gravity  L, 
in  thousand  parts  n,  according  to  the  formula — 

^L— 8.833 
"0.001(5474 

This  method  is  not  adapted  for  very  fine  alloys,  nor  for  such  as 
have  been  cast  and  little  worked  after  the  casting,  as  the  results 
obtained  are  too  high. 

1  Bg.  u.  Httumsch.  Ztg.  1883,  p.  401. 

2  Ztschft.  f.  Anal.  Chem.  Bd.  22,  p.  491. 

3  Dingier,  ccxxiv.  565. 


GOLD — NON-ALLOYS.  161 

IV,  Gold, 

33.    GOLD   ORES. 

Xative  gold,  with  0.1  to  40  per  cent,  of  Ag,  occurring  in  quart- 
zose  veins  (gold  quartz),  and  in  pyrites  (iron  or  copper  pyrites, 
arsenical  pyrites),  and  disseminated  in  alluvial  deposits  (aurifer- 
ous gravel) ;  sylvanite  (Au,  Ag),  Te2,  with  24  to  30  Au  and  3  to 
15  Ag;  nagyagite,  PbTe2  with  PbS  and  AuTe2,  with  6  to  9  Au 
and  50  to  60.5  Pb;  white  tellurium  (Au,Ag,Pb)(Te,Sb)3,  with  24.8 
to  29.6  Au,  2.7  to  14.6  Ag,  and  2.5  to  19.5  Pb. 

34.    NON-ALLOYS. 

Sometimes  mechanical  wash  assays  are  made  use  of  for  an 
approximate  determination  of  the  metallic  gold  contained  in 
poor  earthy  and  gravelly  ores.  Dry  or  fire  assays  (scorification  or 
crucible  assays)  are  mostly  used  for  a  more  accurate  determination 
of  the  percentage  of  gold  in  very  poor  ores ;  and  sometimes  the 
wet  assay  (Plattner's  assay)  also.  The  taking  of  assay  samples 
requires  the  utmost  care  on  account  of  the  very  unequal  distribu- 
tion of  the  gold  in  the  ores  (pp.  19  et  seq.). 

A.  Mechanical  assay  by  washing,  for  determining  the  approxi- 
mate percentage  of  gold  in  earthy  and  gravelly  minerals,  poor  in 
gold.  The  sample  is  rubbed  as  fine  as  possible  and  sifted.  About 
20  grammes  of  it  are  washed  with  water  in  a  vanning  shovel 
(Fig.  5,  p.  27),  until  the  pure  gold  begins  to  show  itself  at  the 
upper  end.  The  quantity  is  either  estimated  or  weighed,  or 
measured  by  bringing  it  into  a  narrow  strip  about  0.36  milli- 
meter wide  (Hungary  and  Transylvania).  Sometimes  it  is  also- 
amalgamated  with  mercury1  and  ignited  in  a  small  crucible 
(Transylvania,  United  States). 

Montana:  5  kilogrammes  of  earthy  gold  ore  are  taken  from 
the  heap,  powdered,  mixed,  and  sifted.  The  coarser  gold  remain- 
ing in  the  sieve  is  weighed  and  assayed  by  itself;  500  grammes 
of  the  fine  sifted  matter  are  placed  in  the  vanning  trough  (or 

i  B.  u.  h.  Ztg.,  1863,  p.  271 ;  1868,  p.  127  ;  1875,  p.  311. 
11 


162  ASSAYING. 

shovel)  (Fig.  5,  p.  27),  mixed  with  some  water  and  5  grammes 
of  mercury,  and  slowly  washed  for  two  hours  (if  the  water  shows 
an  acid  reaction,  some  caustic  soda  is  added),  and  finally  some 
potassium  cyanide  is  added,  and  the  amalgam  completely  purified ; 
mercury  is  removed  by  glowing  the  mass  gently  in  a  crucible  or 
retort.  The  residue  is  cupelled  with  lead,  and  the  alloy  separated 
by  inquartation  and  parting ;  6  to  8  assays  are  made  and  the 
average  is  taken. — Australia:  1  kilogramme  of  gravelly  gold  ore 
is  dead-roasted.  It  is  then  placed  in  an  iron  mortar  and  mixed 
with  water  to  a  stiff  paste.  A  tablespoonful  of  mercury  is  added 
and  thoroughly  rubbed  together  with  the  paste ;  and,  after  a  short 
time,  another  tablespoonful.  The  mass  is  then  washed  in  an 
enamelled  dish,  the  amalgam  collected  and  distilled  off.  This 
method  will  give  from  80  to  90  per  cent,  of  the  quantity  of  gold 
which  would  be  obtained  by  a  fire  assay. 

B.  Fire  or  fusion  assays. — The  object  of  these  assays  is  to 
collect  the  gold  in  the  lead  (smelting  with  lead  by  the  scarification 
or  crucible  assay),  and  to  separate  the  gold  by  duelling  the  aurif- 
erous lead  button.  In  case  the  gold  button  should  contain  any 
silver,  this  can  be  separated  by  the  wet  method  by  means  of  nitric 
acid  (inquartation).  Whether  the  scorification  assay  or  crucible 
assay  is  to  be  chosen  depends  principally  on  the  foreign  admix- 
tures (earth  or  gravel),  and,  as  a  general  rule,  the  same  rules  hold 
good  here  that  were  given  for  silver  ores  (p.  128). 

1 .  Smelting  the  gold  with  lead. 

a.  Scorification  assay  for  ores  of  every  kind. — 0.5  to  10  grammes, 
according  to  the  degree  of  richness  of  the   assay  sample,  are 
weighed,  and  if  the  material  is  poor,  a  sufficient  number  of  assays 
are  made  so  that  the  button  which  is  obtained  does  not  weigh 
less  than  0.05  to  0.20  gramme.     The  same  rule  in  regard  to  the 
quantity  of  granulated  lead  and  borax  is  observed  as  in  the  silver 
assays,  and  the  assays  are  executed  in  the  same  manner. 

b.  Crucible  assay. — Poor,  earthy,  and  oxidized  ores  can  be  as- 
sayed by  this  method  without  preliminary  preparation,  but  those 
containing  sulphur,  antimony,  and  arsenic  must   be  previously 
roasted.     It  is  less  adapted  for  ores  rich  in  gold  and  copper  than 
the  scorification  assay.     It  is  simpler  and  more  convenient,  as  it 
allows  of  operating  with  larger  quantities,  especially  when  the 


GOLD — NON-ALLOYS.  163 

substances  are  poor  in  precious  metal,  and  is  more  accurate  than 
the  scorification  assay,  as  the  losses  are  distributed  among  larger 
quantities  of  assay  sample.  The  assay  sample  is  fused  with 
granulated  lead  or  litharge  and  reducing  and  fluxing  agents. 
The  same  smelting  pots  or  crucibles  (Fig.  52,  p.  65)  are  used  as 
in  the  corresponding  silver  assays.  The  assay  is  fused  in  the 
ordinary  furnace,  or  in  a  gas-furnace. 

a.  Substances  with  earths  and  oxides  (gold  quartz,  slag,  gold 
sweepings). — They  are  fused  in  an  unroasted  condition. 

Sweepings,  as  stated  on  p.  136.  American  gold  ores:  50 
grammes  of  ore,  70  grammes  of  dry  sodium  carbonate,  100  to 
120  grammes  of  litharge  (or  a  corresponding  quantity  of  white 
lead),  and  6  to  8  parts  of  powdered  charcoal.  The  ore,  litharge, 
and  charcoal  are  first  mixed  together,  and  then  with  the  fluxing 
agent ;  and,  in  case  sulphur  should  be  present,  a  small  piece  of 
iron  wire  is  added.  The  charge  is  placed  in  a  smooth  French 
clay  crucible  and  fused  for  half  an  hour  at  an  intense  heat  in  the 
furnace.  It  is  then  poured  out,  after  which  the  crucible  can  be 
used  several  times  more. 

The  results  from  100  pounds  of  gold  quartz  by  the  scorifica- 
tion and  crucible  assay  may  be  given  as  follows : — 

If  100  pounds  of  gold  quartz  give  They  give  by  crucible  assay: 

by  scorification  assay: 

parts  of  pounds.  parts  of  pounds. 

12.5  12.25 

1.5  1.6 

0.14  0.14 

0.09  0.088 

Phcinsand :  500  grammes  of  ore  are  mixed  with  200  grammes 
of  soda,  300  grammes  of  potassium  carbonate,  and  50  grammes 
of  borax.  Upon  this  are  scattered  20  grammes  of  granulated 
lead  free  from  gold  ;  upon  this  come  a  thin  layer  of  soda  and  a 
covering  of  common  salt. 

Assay  with  nothing  but  red  lead  (litharge)  as  flux. — This 
method  can  be  used  with  advantage  with  very  silicious  ores, 
indeed  with  almost  any  ores  when  the  ordinary  fluxes  are  not  at 
hand.  Charge  :  500  grains  (32.4  grammes)  of  ore,  1300  grains 
(84.4  grammes)  of  red  lead,  and  35  grains  (2.33  grammes)  of  char- 


164  ASSAYING. 

coal  are  thoroughly  mixed  and  placed  in  a  crucible.  Place  in  a 
"cold  fire"  and  raise  the  temperature  very  gradually  until  the 
charge  is  thoroughly  fluxed  and  uniform  in  color.  After  pouring 
and  detaching  slag,  the  resulting  lead  button  is  cupelled  in  the 
usual  manner.  If  the  crucible  is  placed  in  a  hot  fire  at  first,  the 
lead  will  be  reduced  without  fluxing  the  ore,  which  will  remain  in- 
tact. The  assay  is  somewhat  difficult  to  make  and  requires  consid- 
erable skill  to  obtain  accurate  results. 

/J.  Ores,  etc.,  with  combinations  of  sulphur,  antimony,  or  arse- 
nic.— Larger  quantities,  0.5  to  1  kilogramme,  are  roasted  so  that 
buttons  weighing  not  less  than  0.05  to  0.20  gramme  are  obtained. 
The  roasting  is  done  in  small  clay  boxes  about  200  millimeters 
long,  70  to  90  millimeters  wide,  and  40  to  50  millimeters  deep. 
The  ore  is  placed  in  these  boxes  and  roasted  in  the  muffle,  being 
carefully  stirred  meanwhile  with  a  stirring  rod.  Or  the  ore  may 
be  placed  upon  a  plate  of  sheet  iron  with  upturned  edges,  which 
has  been  previously  covered  with  a  coating  of  clay,  reddle,  or 
chalk,  and  is  then  roasted  over  a  brazier,  or  in  a  furnace  until  the 
fumes  cease  to  be  evolved  (according  to  Winkler,  Tscheffkin,  and 
Merrick,  a  loss  of  gold  occurs  during  this  operation,  which 
Crookes  denies).1  If  copper  pyrites,  antimony,  and  arsenic  are 
present,  it  is  best  to  add  charcoal  and  ammonium  carbonate  in 
roasting.  The  charging  and  fusing  of  the  roasted  sample  are 
done  in  the  same  manner  as  that  indicated  in  the  assay  for  silver 
(p.  134). 

Pyrites  poor  in  gold. — 500  grammes  of  the  roasted  ore  are 
mixed  with  the  same  quantity  of  granulated  lead  free  from  gold, 
125  grammes  of  black  flux  and  the  same  quantity  of  glass.  The 
charge  is  fused  for  two  hours  in  a  Hessian  crucible  in  .the  furnace. 
The  resulting  button  is  flattened  on  an  anvil  and  cut  up  in  pieces. 
The  separate  pieces  are  concentrated  on  a  scorifier,  and  the  button 
thus  obtained  is  cupelled.  500  grammes  of  ore  are  roasted  and 
mixed  with  125  to  250  grammes  of  potassa  or  soda  glass,  125 
grammes  of  black  flux,  or  250  grammes  of  potassium  carbonate, 

1  [Such  losses  are  undoubtedly  apt  to  occur  in  the  presence  of  tellurides,  and 
in  some  cases  in  roasting  with  common  salt  (sodium  chloride).  See  the 
Losses  in  Roasting  Gold-Ores  and  the  Volatility  of  Gold.  S.  B.  Christy, 
Trans.  Am.  Inst.  M.  E.  vol.  xvii.  p.  3. — Gr.] 


GOLD — XOX- A  LLOYS.  165 

and  32  grammes  of  flour,  then  covered  with  500  grammes  of 
granulated,  lead  free  from  silver,  and  a  layer  of  common  salt.  The 
entire  charge  is  put  in  a  Hessian  crucible  and  fused  for  two  hours 
in  the  furnace,  or  it  is  distributed  into  several  smaller  crucibles. 

Tailings  containing  a  small  amount  of  auriferous  pyrites. — 
Roasting  can  be  dispensed  with  and  the  pyrites  decomposed  by  a 
piece  of  iron  (hoop)  placed  in  the  bottom  of  the  crucible. 

Ore 1000  grains  (64.80  grammes) 

Litharge        .         .         .         .  500      "       (32.40         "       ) 

Sodium  carbonate          .         .  1200      "       (77.77         :<       ) 

Charcoal       .         .         .         .  30      "       (  1.95         "       ) 

Instead  of  using  the  iron  the  ore  may  be  roasted  and  one-third  of 
the  sodium  carbonate  replaced  with  borax. 

Hungarian  smelting  works :  1  Vienna  pound  (=  560  grammes) 
of  the  auriferous  substance  is  roasted  upon  a  clay  plate  over  glow- 
ing coals.  The  charge  consists  of  3  pounds  (=  1680  grammes) 
of  Villaeh  red  litharge,  2  pounds  (=  1120  grammes)  of  dry 
potash,  J  pound  (=  140  grammes)  of  resin,  and  1  loth  (=  14.5 
grammes)  of  hard  coal.  This  is  mixed  and  distributed  in  cruci- 
bles in  such  a  manner  that  on  the  bottom  comes  first  a  spoonful 
of  the  mixture,  and,  upon  this,  a  spoonful  of  the  roasted  sample. 
These  are  then  mixed  together ;  upon  this  mixture  is  placed  an- 
other spoonful  of  the  mixed  fluxes,  and  then  a  covering  of  com- 
mon salt.  115  to  125  crucibles  charged  in  this  manner  are  heated 
for  from  20  to  30  minutes  in  the  furnace,  or  a  small  number  in 
the  muffle.  The  resulting  buttons  are  partly  cupelled,  and  those 
buttons  which  have  not  brightened  are  wrapped  up  in  a  cornet  of 
lead  foil  and  cupelled  together.  The  auriferous  silver  obtained 
must  weigh  about  10  mint  pounds  assay  weight,  and  the  gold 
buttons  to  be  separated  from  this  about  0.1  mint  pound.  Average 
difference  0.001  mint  pound. 

Gold  ores  containing  tellurides. — These  ores  should  be  roasted 
in  the  most  careful  manner,  as,  according  to  Kustel,1  as  much  as  20 
per  cent,  of  the  gold-content  may  be  lost  in  this  way,  due  to  the 
volatilization  of  the  tellurium.  The  difficulties  arising  from  the 

i  Roasting  of  Gold  and  Silver  Ores,  1880,  p.  57. 


166  ASSAYING. 

presence  of  tellurium  in  the  ores  are  best  overcome  by  using  plenty 
of  lead,  the  amount,  of  course,  being  proportioned  to  the  richness 
of  the  ores.  In  cases  of  very  rich  ores  as  much  as  from  75  to  100 
parts  of  lead  may  be  used.  In  such  cases  unusually  large  scorifiers 
must  be  used  or  else  several  of  the  ordinary  size. 
Brown1  recommends  the  following  charge  : — 

Ore 48  grains  (2.5  grammes)  * 

Granulated  lead       .        .         .960      "       (60.0        "       ) 
Litharge  .         .         .         .       48      "       (  2.5         "       ) 

Borax  glass      .         .         .         .        4      "      (  0'.25       "       ) 

Sprinkle  litharge  over  the  mixed  charge.  The  buttons  may  need 
repeated  scorifications  with  plenty  of  lead. 

2.  Cupellation  of  the  auriferous  lead. — The  process  is  the  same 
as  for  silver  with  the  exception  of  a  hotter  "  driving"  towards  the 
end  of  the  assay,  so  that  no  plumose  litharge  (Federglatte)  re- 
mains. If  the  assay  sample  is  poor,  the  separate  lead  buttons  are 
either  entirely  cupelled  or  only  partly.  In  the  latter  case  they 
are  wrapped  in  lead  foil  and  cupelled  together.  The  resulting 
gold  button  is  then  weighed,  and,  in  case  it  contains  silver,  this 
is  parted  by  means  of  nitric  acid.  We  shall  only  briefly  mention 
the  process  here,  as  it  will  be  more  thoroughly  explained  later  on 
in.  treating  of  gold  and  silver  alloys  (§  35). 

The  button  is  flattened  out  on  the  anvil  and  placed '  in  a  flask 
with  a  very  narrow  neck,  and  then  heated  with  nitric  acid  of 
1.19  specific  gravity,  a.  When  the  laminated  button  breaks  up 
and  brown  flakes  of  gold  are  separated,  this  being  an  indication 
that  a  sufficient  quantity  of  silver  is  present ;  the  heating  is  in- 
terrupted when  no  more  nitrous  acid  is  developed.  The  gold  is 
allowed  to  settle,  and  the  liquid  is  then  carefully  decanted.  It  is 
now  washed  twice  by  decantation  with  boiling  distilled  water. 
The  flask  is  then  entirely  filled  with  cold  water  and  inverted  in  a 
clay  crucible,  or  a  small  porcelain  saucer,  and  when  the  gold  has 
dropped  into  the  crucible,  the  flask  is  carefully  withdrawn  over  the 
side.  The  water  is  then  poured  off,  the  gold  dried,  the  crucible 
then  strongly  heated,  and  finally  the  adherent  gold  is  removed 
and  weighed,  b.  When  the  flattened  button  does  not  break  up, 

1  Manual  of  Assaying,  Chicago,  1886,  p.  188. 


ALLOYS   OF   GOLD.  167 

the  acid  is  poured  off  and  the  sample  decanted  with  cold  water. 
The  flask  is  filled  with  cold  water  and  inverted  in  a  porcelain 
dish  and  withdrawn  over  the  side.  After  the  water  has  been 
poured  off,  the  button  is  dried  and  wrapped,  with  three  times  the 
quantity  of  silver,  in  a  cornet  of  lead  foil  or  with  granulated  lead 
in  a  cornet,  and  cupelled.  The  button,  containing  now  a  suffi- 
cient quantity  of  silver,  is  parted  with  nitric  acid.  In  the  Upper 
Harz  the  percentage  of  gold  is  not  taken  int,o  calculation  when 
10  assay  centner  (=50  grammes)  contain  less  than  0.5  part  of 
a  pound  (=  .25  milligramme)  of  gold.  The  buttons  obtained 
from  gold  ores  are,  as  a  rule,  richer  in  gold  than  in  silver,  and 
require  an  addition  of  2  to  2J  times  the  quantity  of  silver,  while 
those  from  auriferous  silver  ores,  pyrites,  and  matt  contain  gene- 
rally less  than  J  to  J  of  gold  and  require  no  addition  of  silver. 

C.  Wet  assay  (Plattner's  chlorination  process1). — This  is  some- 
times used  for  very  poor  ores.  50  to  200  grammes  of  earthy  or 
oxidized  ore,  or  completely  roasted  pyrites,  are  slightly  moistened 
with  water  and  placed  in  a  tubulated  glass  cylinder,  the  bottom 
of  the  vessel  being  first  covered  with  pieces  of  quartz.  Here 
they  are  treated  with  chlorine  gas  for  about  one  hour.  The  gold 
chloride  formed  is  lixiviated  with  hot  water,  and  the  solution 
heated  to  expel  the  free  chlorine.  Solution  of  ferrous  sulphate 
and  some  hydrochloric  acid  is  added,  which  precipitates  the  gold 
in  a  metallic  state.  It  is  then  filtered  and  washed,  the  filtrate  is 
dried  and  cupelled  with  5  to  10  grammes  of  granulated  lead. 
\Vayner  recommends  the  decomposition  of  the  ores  with  bromine2 
instead  of  chlorine. 

• 

35.    ALLOYS  OF  GOLD. 

The  principal  alloys  of  gold  which  will  be  especially  considered 
here  are  those  with  silver,  with  silver  and  copper,  and  with  copper. 

Gold  amalgam  is  distilled  in  a  glass  retort,  and  the  residue  is 
carefully  scorified  with  8  parts  of  granulated  lead  (p.  132). 
Auriferous  lead  and  bismuth  are  directly  cupelled,  but  if  they 
contain  too  small  a  quantity  of  gold,  they  are  first  slagged  off  on 

1  Plattner-Richter's  Lotlirohrprobirkuust,  1865,  p.  546. 

2  Dingier,  ccxix.  544. 


168  ASSAYING. 

a  scorifier  (p.  64).  Auriferous  iron,  stee1,  etc.,  are  dissolved  in 
nitric  acid  and  evaporated  to  dryness.  The  dry  mass  is  scorified 
with  8  to  10  parts  of  granulated  lead  and  some  borax. 

A.  Alloys  of  gold  and  silver,  with  or  without  copper. — The  sepa- 
ration of  gold  from  silver  (called  "  quartation"  on  account  of  the 
proportion  of  gold  to  silver  as  1  :  3)  is  done  by  means  of  nitric 
acid.1  But  the  silver  is  only  completely  dissolved  by  boiling  the 
acid  three  times,  and  when  at  least  2J  to  3  parts  of  silver  are 
present  to  1  part  of  gold.  When  this  proportion  exists,  the  gold 
will  also  be  obtained  in  a  cohering  mass  having  the  same  form  as 
that  of  the  alloy  used  (a  small  roll,  etc.*).  If  less  silver  is  present, 
the  gold  remains  argentiferous,  and  if  more,  for  instance,  4  to  6 
silver  to  1  gold,  the  gold  is  obtained  in  brownish  flakes  or  as 
powder  (dust  gold),  while  the  silver  will  be  completely  dissolved 
by  boiling  the  assay  twice  with  nitric  acid,  and  there  is  great 
liability  that  mechanical  losses  will  occur.  If  the  silver  is  to  be 
dissolved  by  boiling  the  assay  but  once  with  nitric  acid,  at  least 
8  parts  of  silver  to  1  part  of  gold  must  be  present.  A  prelimi- 
nary assay  is  therefore  required  for  an  approximate  determina- 
tion of  the  percentage  of  gold,  to  enable  the  assayer  to  fix  the 
required  quantity  of  silver  which  must  be  added,  and  also  for 
the  determination  of  the  percentage  of  copper,  in  order  to  find 
the  quantity  of  lead  required  to  be  added  to  it  in  removing  it  by 
cupellation. 

1.  As  a  preliminary  test  for  alloys  free  from  copper,  may 
serve — 

a.  The  color  of  the  alloy. — A  deep  yellow  color  requires  2J  to 
3  times  the  quantity  ;  light  yellow,  twice  the  quantity  ;  and  a 
white  color  an  equal  weight  of  quartation  silver. 
-  For  an  approximate  determination,  by  color,  of  the  richness 
of  the  gold  button,  sample  gold-silver  buttons  2  to  3  millimeters 
in  diameter  have  been  prepared  with  •£•§-,  y9^,  r^-,  T77,  T6^,  and  T% 
of  gold.  They  are  placed  in  depression  in  a  box  with  a  cover, 
and  each  is  surrounded  with  a  black  ring  and  then  with  a  white 
one.  Before  the  comparison  is  made,  the  assay  button  is  breathed 

[!  This  proportion  varies  ;  some  assayers  prefer  1  :  2£.  According  to  Pet- 
tenkofer,  the  proportion  need  not  exceed  1  :  !£,  provided  the  subsequent  boil- 
ing in  HN03  is  sufficiently  prolonged. — G.] 


ALLOYS   OF   GOLD.  169 

on,  as  otherwise  its  strong  lustre  would  make  the  estimation  less 
accurate.  GoMxehmuU1  has  attached  similar  specimen  alloys,  in 
the  form  of  small  disks  upon  porcelain,  but  it  is  more  difficult 
to  compare  the  buttons  with  these  than  with  sample  buttons  of 
the  same  shape.  If  more  than  56  per  cent.  Ag  is  present,  the 
gold  cannot  be  recognized.  2  per  cent,  of  Ag  imparts  a  brass 
color,  50  per  cent,  a  light  yellow,  and  56  per  cent,  a  white  color 
to  the  gold. 

b.  An  examination  on  the  touchstone  by  means  of  needles,  touch- 
stone, and  nitric  acid  requires  more  experience  than  the  above 
method,  and  may  also  be  used  for  alloys  containing  copper. 

2.  Preliminary  assay  of  cupriferous  alloys  by  cupellation. 

a.  With  lead  alone. — 250  milligrammes  of  the  alloy  cut  up 
into  fine  shreds  or  granulated  are  weighed  off  and  wrapped  up 
in  a  cornet.  This  is  placed  with  16  to  32  times  the  quantity  of 
lead  (4  to  8  grammes,  according  to  the  percentage  of  copper)  in 
one  piece  (spherical  or  hemispherical)  in  a  strongly  glowing  cupel 
in  the  furnace.  The  cupellation  is  conducted  in  the  same  man- 
ner as  with  the  fine  assay  (p.  144),  except  that  it  must  "drive  " 
hotter,  so  that  no  plumose  litharge  (Federglatte)  remains.  The 
percentage  of  copper  is  found  from  the  difference  in  the  weight 
of  the  alloy  used  and  the  resulting  auriferous  silver  button.  An 
experienced  assayer  can  then  estimate  the  richness  of  the  alloy 
in  gold  by  the  color  of  the  button  after  breathing  on  it,  and  can 
thus  calculate  the  quantity  of  quartation  silver  to  be  added  for 
the  principal  assay.  The  quantity  of  lead  required  for  remov- 
ing the  copper  by  cupellation  will  be  indicated  from  the  differ- 
ence in  weight. 

The  quantity  of  lead  to  be  taken  depends  on  the  percentage  of 
copper  in  the  alloy,  which  must  be  removed  before  the  quartation. 
As  copper  has  a  greater  affinity  for  gold  than  for  silver,  argenti- 
ferous gold  containing  copper  requires  a  larger  quantity  of  lead 
in  cupelling  (the  maximum  is  32  times  the  quantity)  than  argen- 
tiferous copper  (16  to  20  times  the  quantity). 

The  following  table  (Table  I.)  sliows  the  quantity  of  lead  re- 
quired for  alloys  of  gold  with  silver  and  copper  : — 

1  Fresenius's  Ztschr.  xvii.  142.     B.  u.  h.  Ztg.  ISIS,  p.  208. 


170 


ASSAYING. 


Table  I. 


If  the  gold  in  1000  parts 
of  the  alloy  amounts  to 
1000 

980  to  920 
920  "  875 
875  "  750 
750  "  600 
600  "  350 
350  "  0 


Equivalent 

to  gold. 
24  carat. 
23£to  22 
22    "    21 
21 
18 
14 


18 
14 
.8 
0 


Multiples  of 
lead. 

8 

12 
16 
20 
24 
28 
32 


Table  II.  gives  the  quantity  required  if  the  percentage  of 
gold  is  very  small. 

Table  II. 


If  the  silver  iu  1000 

parts  amounts  to 

1000  to  950 

950  "  900 

900  "  850 

850  "  750 

750  "  650 

650  "  0 


Equivalent  to 

silver. 

15  loth  9  gran. 
14     "    9     " 
13     "    9     " 
12     " 
11     " 


10 


and  less 


Multiples  of 
lead. 

4 

6 

8 

12 
14 
16 


b.  With  an  addition  of  lead  and  silver. — This  process  is  made 
use  of  to  avoid  the  estimation  of  the  quantity  of  gold  in  the 
auriferous  silver  button  by  the  color.  250  milligrammes  of  the 
alloy  are  wrapped  up  in  a  cornet,  together  with  3  times  the 
quantity  of  silver  (750  milligrammes),  and  16  to  32  times  the 
quantity  (4  to  8  grammes)  of  lead,  and  cupelled.  The  loss  of 
copper  is  found  from  the  diiference  in  weight  between  the  re- 
sulting button  and  the  alloy  weighed  plus  the  addition  of  silver. 
The  auriferous  silver  button  is  laminated  and  placed-  in  a  flask 
with  a  long  and  narrow  neck  which  has  been  previously  well 
cooled  off.  The  matrass  should  be  from  150  to  180  millimeters 
high,  30  to  50  millimeters  wide  in  the  belly,  and  6  to  8  milli- 
meters in  the  neck.  The  button  is  boiled  in  this  with  pure  nitric 
acid  of  1.19  specific  gravity  until  no  more  red  vapors  are 
Devolved,  and  is  then  washed  twice  by  decantation  with  hot  water. 
The  flask  is  then  entirely  filled  with  water,  a  small  crucible  of 
clay  placed  over  its  mouth,  and  both  crucible  and  flask  are  in- 
verted, which  cause  the  gold  in  the  form  of  a  small  flake  or 


ALLOYS   OF   GOLD.  171 

powder  to  fall  into  the  crucible.  The  flask  is  now  raised  and 
quickly  drawn  away  over  the  edge  of  the  crucible.  The  gold 
is  then  thoroughly  dried  by  igniting  it  in  the  crucible.  Its 
weight,  plus  that  of  the  added  quartation  silver,  deducted  from 
the  weight  of  the  auriferous  silver  button  originally  employed, 
gives  the  percentage  of  silver  in  the  original  alloy,  according  to 
which,  the  addition  of  silver  for  the  assay  must  be  regulated  so 
that  the  proportion  of  1  An  to  2J  or  3  Ag  is  maintained.  For 
coins,  the  standard  of  which  is  known,  such  preliminary  assays 
are  not  required. 

German,1  French,  and  American  gold  coins  contain  900  Au 
and  100  Cu ;  Austrian  ducats  986,  Prussian  Friedrichsdor  902, 
English  sovereigns  916,  Hanoverian,  Brunswick,  and  Danish  pis- 
toles 896  parts  of  gold.  Pare  gold  is  prepared  by  dissolving 
ducat  gold,  or  gold  cupelled  with  lead  and  laminated,  in  cold 
aqua  regia  (2  parts  of  hydrochloric  and  1  part  of  nitric  acid),  by 
adding  the  acid  gradually,  so  that,  when  the  solution  is  complete, 
there  will  be  no  excess  of  aqua  regia.  The  solution  is  allowed 
to  stand  for  several  days,  for  the  silver  chloride  to  settle,  and  is 
then  filtered.  It  is  now  diluted,  and  if  necessary,  again  filtered 
in  a  few  days.  The  filtrate  is  much  diluted,  and  freshly  prepared 
solution  of  ferrous  sulphate  added  to  it  until  no  more  gold  is 
precipitated,  and  then  allowed  to  stand  in  a  warm  place.  The 
fluid  is  then  removed  by  means  of  a  siphon,  the  gold  placed  in 
a  porcelain  dish  and  digested  with  diluted  hydrochloric  acid. 
The  dried  powder  is  washed,  placed  in  a  clean  clay  crucible,  and 
fused  with  some  borax  and  saltpetre. 

Roberts2  recommends  the  following  process  for  the  preparation 
of  chemically  pure  gold. — The  purest  gold  that  can  be  obtained  is 
dissolved  in  HCl-}-HNO3.  Evaporate  to  dryness,  add  potassium 
chloride  and  alcohol,  to  precipitate  platinum,  take  up  with  pure  dis- 
tilled water  and  dilute  solution  until  each  gallon  does  not  contain 
over  one-half  ounce  of  gold.  The  solution  is  allowed  to  stand  for 
several  weeks;  some  silver  chloride  will  separate  out  and  fall  to 
the  bottom  of  the  vessel.  Siphon  or  decant  off  the  supernatant 

1  Goldner,  Farbe  der  Zwanzig  Mark  Stuke  in  Dingier,  ccviii.  75. 

2  Fourth  Annual  Report  of  Royal  Mint,  1874,  p.  46. 


1 72  ASSAYING. 

liquid,,  and  precipitate  the  gold  with  carefully  washed  sulphurous 
acid.  Ferrous  sulphate,  oxalic  acid  or  formic  acid  may  also  be 
used  for  this  purpose.  Wash  precipitate  repeatedly  with  hot  dis- 
tilled water,  HC1  and  ammonium  hydrate,  and  finally  with  pure 
distilled  water.  Fuse  in  clay  crucible  with  potassium  bisulphate, 
and  borax.  This  gold  will  be  (according  to  Roberts)  999.96  fine. 
Gold  precipitate  from  an  acid  solution  containing  copper  by  oxalic 
acid  is  apt  to  be  contaminated  with  cupric  oxalate.  According  to 
Purgotti,1  however,  if  the  solution  is  heated  with  potash,  a  soluble 
double  oxalate  of  copper  and  potash  is  formed,  and  the  gold  left 
pure. 

I.  Roll  assay  for  argentiferous  gold. — This  requires  the  follow- 
ing manipulations  : — 

a.  Preliminary  assay  as  described  on  p.  168  for  determining 
the  percentage  of  gold  and  copper  in  order  to  fix  the  quantity  of 
quartation  silver  and  lead  to  be  added. 

b.  Weighing  the  assay  sample. — Two  samples  of  the  alloy,  gran- 
ulated or  laminated  and  cut  into  fine  shreds,  each   250  milli- 
grammes, are  accurately  weighed  out  upon  an  assay  balance  which 
must  be  sensitive  to  0.1  milligramme.     If  bars  are  to  be  assayed, 
a  sample  of  250  milligrammes  each  is  cut  from  the  upper  and 
lower  side  from  opposite  ends.     The  samples  are  wrapped   in 
cornets. 

G.  Charging. — The  quantity  of  silver  required  is  weighed  off, 
cut  up  into  fine  shreds,  and  added  to  the  sample.  The  quantity 
must  be  ogjjgulated  or  found  from  tables  according  to  the  results 
of  the  preliminary  assay.  The  lead  is  next  weighed  off  in  one 
piece  according  to  Table  I.  p.  170. 

d.  Cupelling. — The  lead  is  placed  in  thoroughly  ignited  fine 
cupels  standing  alongside  of  each  other  in  the  centre,  or  more  to- 
wards the  back  of  a  strongly  heated  mint  furnace  (Fig.  30,  p.  49). 
The  mouth  of  the  muffle  is  closed  until  the  lead  "drives,"  when 
it  is  opened,  and  the  cornets  containing  the  alloy  are  placed  in 
the  cupel.  The  mouth  of  the  muffle  is  again  closed,  and  the  as- 
say is  allowed  to  "  drive,"  and  the  operation  further  conducted  in 
the  same  manner  as  in  the  fine  assay  (p.  144),  with  the  exception  of 

1  Zeitschr.  Anal.  Chem.,  vol.  9,  p.  127. 


ALLOYS   OF   GOLD.  173 

a  stronger  heat  towards  the  end.     Of  the  loss  of  gold  in  cupelling 
we  will  speak  later  on. 

If  fine  gold  with  990  thousandths  "drives"  too  hot,  or  too  cold, 
the  resulting  gold  button  will  be  one-thousandth  too  heavy.  This 
is  very  likely  caused  by  some  lead  which  remains  with  the  gold, 
and  which  cannot  be  completely  removed  by  nitric  acid.  For 
this  reason  a  sample  of  pure  gold  is  generally  cupelled  with  the 
same  quantity  of  lead  at  the  same  time  as  the  principal  assay,  and 
the  gain  in  weight  of  the  fine  gold  is  then  deducted  from  the  gold 
percentage  of  the  principal  assay.  If  the  button  has  been  bright- 
ened too  hot,  it  is  apt  to  crack  in  laminating. 

e.  Flattening  (laminating)  the  button. — The  button  is  removed 
by  means  of  a  pair  of  pliers,  brushed  oif,  and  the  edges  care- 
fully pinched  with  the  pliers  to  remove  any  adhering  particles 
of  bone  ash  of  cupel.1  It  is  then  laminated  with  a  hammer  on 
a  polished  steel  anvil,  having  a  diameter  of  6  to  8  centimeters. 
The  head  of  the  hammer  has  on  one  end  a  round  or  square  face, 
smoothly  polished,  and  about  4  centimeters  (1.57  inches)  in  di- 
ameter, and  on  the  other  end  a  rounded-off  edge.  Or,  the  button 
after  it  has  been  somewhat  flattened  on  the  anvil  is  passed  be- 
tween rollers,  being  frequently  annealed  meanwhile  on  a  cupel, 
or  dish,  in  the  muffle.  The  small  oval  leaf,  into  which  it  is 
laminated,  is  about  25  millimeters  long,  12  millimeters  wide,  and 
0.5  millimeter  thick.  The  frequent  annealing  of  the  button  and 
hammering  of  the  edges  are  required  to  prevent  the  leaf  from 
cracking  on  the  edges.  If  necessary,  the  leaves  are  numbered 
by  means  of  a  punch  and  hammer.  After  having  been  annealed 
once  more,  the  leaves  are  rolled  with  a  pair  of  pliers  and  dry- 
fingers,  into  the  form  of  a  spiral,  or  over  a  glass-rod,  into  a  small 
roll. 

This  "  flattening"  operation  of  the  button  a  (Fig.  76)  should  be 
very  carefully  done  and  requires  some  skill.  The  first  blow  is 
struck  on  the  centre,  then  on  the  edge,  and  a  third  blow  on  the  op- 
posite edge,  which  elongates  the  metal.  After  annealing,  the  flat- 
tened button  is  rolled  into  a  thin  leaf  c,  and  then  into  a  cornet  or 
spiral  d.  After  boiling  in  HN03  the  bulk  is  considerably  reduced 

1  [Immersioii  in  warm  dilute  hydrochloric  acid  will  also  answer. — G.] 


174 


ASSAYING. 


as  e.  Care  should  be  observed  in  rolling  up  the  cornets  that  the 
outer  surface  should  be  that  which,  before  flattening,  was  in  contact 
with  the  cupels. 

Fig.  76. 


a 


\J 


f.  Soiling  in  nitric  acid. — One  or  more  of  the  numbered  rolls 
are  placed  in  a  long-necked  glass  flask,  about  150  to  180  milli- 
meters long,  with  a  body  width  of  40  to  50  millimeters,  and  a 
neck  width  of  15  to  20  millimeters.  Here  they  are  heated  with 
a  quantity  of  nitric  acid  (about  10  grammes)  sufficient  to  fill  the 
body  of  the  flask  half-full.  The  acid  should  be  of  1.2  specific 
gravity,  as,  if  it  is  stronger,  its  action  might  be  too  violent  and 
tear  the  leaf.  It  should  be  free  from  nitrous  acid,  sulphuric  acid, 
and  chlorine,  and,  if  necessary,  is  freed  from  chlorine  by  adding 
some  solution  of  silver  nitrate.  The  leaves  are  heated  until  the  fumes 
of  nitrous  acid  have  disappeared.  Bumping  during  the  ebullition 
is  prevented  by  throwing  a  small  splinter  of  coal,  or,  what  is  still 
better,  a  completely  carbonized  pepper-corn,  into  the  flask.1 

The  flask  is  lifted  from  the  fire  by  means  of  a  wooden  clamp, 
and  the  solution  of  silver  carefully  poured  into  a  porcelain  dish. 
Nitric  acid  of  1.3  specific  gravity,  previously  heated  to  boiling, 
is  now  poured  upon  the  leaves,  and  they  are  again  boiled  for  10 
minutes.  The  pouring  off  of  the  solution  is  repeated,  and  the 
leaves  are  again  boiled  for  10  minutes,  with  fresh  strong  nitric 


i  Polyt.  Ctrbl.  1857,  p.  314.     B.  u.  h.  Ztg.  1861,  p.  407. 
[Small  pellets  or  peas  of  burnt  clay  are  better. — G.] 


ALLOYS   OF   GOLD.  175 

acid,  previously  boiled.  This  third  boiling  is  sometimes  omitted, 
if  the  percentage  of  gold  is  below  750  thousandths.  After  the 
third  boiling,  according  to  Kandelhard's  experiments,  such  a 
small  residue  of  silver  remains  in  the  gold,  that  it  is  equalized  by 
the  loss  caused  by  cupellation,  and  the  result  will  be  correct. 

(The  heating  may  be  done  by  placing  a  single  flask  upon  a 
support,  with  three  legs,  and  provided  with  a  handle,  over  a  lamp, 
or  upon  glowing  coals.  If  several  flasks  are  used  at  one  time, 
they  may  be  placed  in  depressions  in  the  periphery  of  a  sheet- 
metal  disk,  which  are  filled  with  sand,  and  furnished  with  clamps 
for  holding  the  necks  of  the  flasks ;  or,  they  are  placed  upon  a 
movable  support,  with  a  gas-pipe  and  burners  throwing  out  lateral 
flames ;  or  upon  Levol's  gas-heating  apparatus.  Matthcy  and 
Johnson's1  new  platinum  apparatus  permits  of  many  rolls  (10  to 
100)  being  boiled  at  one  time  in  small  thimble-like  crucibles, 
which  are  immersed  in  the  acid.  It  is  highly  recommended  on 
account  of  its  great  convenience  and  cleanliness,  and  saving  of 
acid.  Tookey2  uses  a  platinum  tube  for  heating.) 

By  dissolving  silver  in  nitric  acid,  nitrous  acid  is  formed  which 
does  not  attack  the  gold  as  long  as  silver  is  present.  But  it  will 
do  so  if  it  is  developed  after  the  silver  has  been  removed.  Such 
development  may  be  caused  by  the  action  of  the  splinter  of  wood- 
charcoal  placed  in  the  flask  to  prevent  bumping  during  ebullition, 
in  case  it  should  contain  any  woody  substance.  For  this  reason, 
it  is  best  to  avoid  the  use  of  charcoal  for  this  purpose. 

g.  Washing  (rinsing  off)  the  rolls. — After  the  last  boiling  with 
nitric  acid,  the  acid  is  poured  off,  and  hot  distilled  water  is  allowed 
to  flow  slowly  into  the  flask  from  a  copper  kettle,  the  spout  of 
which  is  introduced  into  the  neck  of  the  flask,  or,  what  is  still 
better,  from  a  glass  pitcher.  While  the  water  is  running  into  the 
flask  the  latter  should  be  constantly  turned,  until  it  is  about 
f  full  of  Avater.  The  water  is  then  poured  out,  and  this  operation 
is  twice  repeated,  until  the  last  traces  of  silver  nitrate  are  removed 
from  the  roll  and  the  sides  of  the  flask.  The  flask  is  now  filled 
entirely  full,  a  small  crucible  glazed  inside,  or  a  porcelain  cup  or 

1  B.  n.  h.  Ztg.  1870,  p.  325. 

[See  Percy,  Metallurgy  of  Silver  and  Gold,  vol.  i.  p.  263.— G.] 

2  Dingier,  cxcvii.  93.     B.  u.  h.  Ztg.  1870,  p.  283. 


176  ASSAYING. 

saucer,  is  placed  over  its  mouth,  and  both  cup  and  matrass  in 
this  position  are  slowly  inverted,  which  causes  the  roll  to  gradu- 
ally slide  down  into  the  cup  or  crucible.  The  flask  is  then  drawn 
away  over  the  edge  of  the  crucible,  after  which  the  water,  now  no 
longer  showing  a  silver  reaction  with  hydrochloric  acid,  is  poured 
from  the  crucible. 

h.  Drying  and  annealing  of  the  rolls. — They  are  thoroughly 
dried  in  crucibles,  which  are  covered  and  placed  on  the  shelf  in 
front  of  the  muffle,  or  into  the  »round  holes  of  a  metal  plate,  into 
which  they  fit.  The  feet  of  this  plate  stand  upon  a  sheet-metal 
plate,  heated  by  glowing  coals  from  below.  The  rolls,  which  are 
of  a  brownish  color  and  porous,  are  now  heated  in  the  same 
crucibles  in  the  muffle-furnace  at  a  white  heat,  whereby  they 
must  assume  the  lustre  and  color  of  gold,  after  which  they  are 
taken  from  the  crucibles. 

i.  Weighing  of  the  rolls. — After  the  rolls  have  become  cool,  they 
must  be  quickly  weighed,  as  they  easily  absorb  gases.  A  roll, 
and  another  from  a  check  assay  are  laid  on  the  opposite  pans  of 
a  balance.  If  they  agree  (in  assays  from  the  upper  and  lower 
side  of  a  bar,  differences  may  occur),  they  are  both  weighed,  and 
the  percentage  of  gold  is  thus  determined.  The  average  is  taken 
of  the  upper  and  lower  assay.  (It  is  customary  to  give  the  lowest 
percentage  of  fine  assays  of  silver,  p.  146.) 

A  loss  of  gold  occurs  in  cupelling,  partly  on  account  of  the 
volatilization  of  gold  with  other  metals  and  partly  by  absorption 
by  the  cupel  (Kapellenzug).  According  to  Kandelhard,  this  loss 
is  equalized  by  the  retention  of  a  residue  of  silver  in  the  roll, 
but  this,  according  to  Rossler,1  is  not  always  the  case,  as  differ- 
ences may  occur  between  the  found  and  actual  percentage  of  gold, 
from  a  cooler  or  hotter  "brightening"  and  in  alloys  of  different 
proportions.  According  to  Kandelhard's  method,  the  residue  of 
silver  in  the  roll  is  1  thousandth  when  2  J  parts  of  silver  to  1 
part  gold  have  been  used  in  the  quart  at  ion,  and  the  alloy  has 
been  boiled  three  times;  1.5  to  2.5  thousandths  if  boiled  not  quite 
so  thoroughly,  and  up  to  5  thousandths  if  boiled  but  once. 
According  to  Bossier,  the  loss  of  gold  by  cupelling  increases  with 

1  Dingier,  ccvi.  185.     B.  u.  h.  Ztg.  1873,  p.  26. 

• 


ALLOYS   OF   GOLD.  177 

the  quantity  of  lead  used  (when  J  gramme  of  gold  is  cupelled 
with  1  to  2  grammes  of  lead,  the  loss  is  only  fractions  of  a 
thousandth  •  when  4  to  8  grammes  of  lead  are  used,  it  is  over 
2  thousandths,  even  if  a  residue  of  silver  of  nearly  1  thousandth 
is  taken  into  consideration).  The  loss  is  also  greater  the  smaller 
the  gold  button  is  (therefore  also  when  a  smaller  quantity  of  the 
sample  is  weighed)  and  the  smaller  the  quantity  of  silver  (accord- 
ing to  Bossier,  1  to  3  thousandths  of  pure  gold  are  lost  if  4  times 
the  quantity  of  lead  is  used  in  the  quartating  cupellation ;  if  the 
button  contains  more  than  2J  times  the  quantity  of  silver,  the 
residue  of  silver  commences  to  preponderate,  and  with  a  large 
quantity  of  silver  it  seems  to  be  almost  in  excess).  According  to 
this,  assays  with  a  small  percentage  of  gold  cupelled  with  much 
lead  would,  under  otherwise  equal  conditions,  come  out  some- 
what worse  than  those  with  a  high  percentage,  and,  if  losses  of 
gold  and  residue  of  silver  equalize  each  other,  the  loss  would 
preponderate  in  all  smaller  assays. 

An  English  commission1  having  caused  an  examination  to  be 
made  of  samples  of  different  coins  with  an  accurately  determined 
percentage  of  gold,  the  errors  in  the  assay  were  found  to  amount 
to  from  T^OTJT  to  T-^ w  per  cent. 

Platinum  renders  the  surface  of  the  auriferous  silver  button, 
after  it  has  been  cupelled,  crystalline,  porous,  and  rough,  and,  if 
much  of  it  is  present,  gray.  It  is  removed  by  cupelling  the 
button  resulting  from  quartation,  after  it  has  been  weighed,  with 
8  times  the  quantity  of  silver  and  lead,  and  treating  the  result- 
ing button,  after  it  has  been  laminated,  with  nitric  acid  until  the 
weight  of  the  roll  remains  constant  and  platinum  is  no  longer 
dissolved  with  the  silver.2  Rhodium  and  iridium  produce  black 
stains  upon  the  auriferous  silver  buttons  after  the  brightening, 
and,  if  a  large  percentage  of  iridium  is  present,  the  rolls  break 
and  black  iridium  powder  will  be  found  between  the  gold.  The 
gold  is  then  dissolved  in  aqua  regia  and  precipitated  with  ferrous 
sulphate. 

1  Report  of  the  British  Association,  1875,  p.  127. 

2  Winkler,   Loslichkeit  von   Platinsilber  in  Salpetersaure  in   Fresenius's 
Ztschr.  1874,  p.  369.     B.  u.  h.  Ztg.  1845,  p.  145. 

12 


178  ASSAYING. 

D'Hennin1  claims  to  separate  the  iridium  by  fusing  12.5 
grammes  of  gold  containing  it  with  3  grammes  of  sodium 
arsenate,  18  grammes  of  black  flux,  and  20  grammes  of  a  flux 
consisting  of  a  mixture  of  borax,  argol,  litharge,  and  charcoal, 
into  a  speiss  containing  iron  and  arsenic,  while  the  gold  and 
silver  are  collected  in  the  lead. 

Palladium  passes  with  the  silver  into  solution,  if  the  gold  con- 
taining it  is  alloyed  with  3  times  the  quantity  of  silver. 

In  cupelling  pure  gold  at  a  temperature  above  its  melting-point 
and  removing  it  from  the  muffle  whilst  still  in  a  fluid  state,  it  shows, 
according  to  Tan  Riemsdijk,2the  phenomenon  of  brightening  (Blick- 
ens)  very  plainly.  The  glowing  gold  cools  at  a  red  heat  without 
changing  its  condition,  and  in  the  course  of  20  to  40  seconds  the 
button  suddenly  emits  vivid  flashes  of  green  light  which  abate  and 
disappear  as  it  cools  and  sets. 

To  obtain  good  results  in  cupelling  gold  the  following  conditions 
must  be  observed : — 

1.  The  cupelling  must  be  effected  at  least  at  the  melting-point  of 
silver. 

2.  The  gold  when  taken  from  the  muffle  must  be  in  a  liquid 
state. 

3.  It  must  show  a  smooth  and  even  surface  and  in  removing  the 
cupel  from  the  muffle  it  must  not  be  shaken. 

4.  The  button  must  cool  uniformly. 

The  phenomenon  of  brightening  being  due  to  the  superheating 
of  the  gold,  it  is  desirable  that  it  contain  a  small  amount  of  copper 
which  promotes  superheating.  A  content  of  more  or  less  silver  is 
detrimental  to  the  appearance  of  brightening  on  account  of  the  ab- 
sorption of  oxygen  by  the  silver,  which  it  again  yields  up  in  cool- 
ing, thus  disturbing  the  internal  quietness  of  the  button  and  render- 
ing the  gold  less  ductile.  In  this  case,  however,  the  brightening  can 
easily  be  produced  by  the  addition  of  a  known  quantity  of  copper. 
An  alloy  consisting  of  250  milligrammes  of  gold,  625  of  silver,  and 
25  of  copper  brightens  very  perceptibly  in  cupelling  with  from  3  to 
3  J  grammes  of  lead.  According  to  the  same  author,  gold  containing 
osmium,  ruthenium,  rhodium,  and  iridium  does  not  brighten  even  if 

1  Dingier,  cxxxvii.  443. 

2  Archiv.  Neerlandaises,  torn.  xv.  p.  185.      Bg.  u.  Huttenm.     Ztg.  1880, 
p.  247. 


ALLOYS   OF   GOLD.  179 

cupelled  at  a  very  high  heat;  thus  the  appearance  of  brightening  in 
this  case  is  a  useful  indication  of  the  purity  of  the  gold. 
Van  Riemsdijk1  further  states, 

1.  That  the  smallest  quantity  of  ruthenium  or  iridosmium  present 
in  the  original  alloy  will  remain  in  the  gold  after  parting  from  silver 
and  cupelling  with  lead. 

2.  The  presence  of  about  0.001  per  cent,  of  iridium  is  not  detri- 
mental to  the  accuracy  of  the  assay,  such  a  small  quantity  being  re- 
moved with  the  silver  in  parting  with  HNO3.     A  content  of  over 
0.001  per  cent,  iridium,  however,  prevents  the  appearance  of  bright- 
ening and  makes  the  buttons  too  heavy. 

3.  No  perceptible  influence  upon  the  brightening  is  caused  by  the 
presence  of  0.002  per  cent,  of  rhodium  ;  a  larger  amount,  however, 
prevents  its  appearance.     Such  buttons  adhere  tightly  to  the  cupel, 
congeal  immediately  on  removing  from  the  muffle,  have  a  rose  color, 
and,  in  proportion  to  the  amount  of  rhodium  present,  are  red  brown 
or  blackish. 

4.  A  very  small  content  of  osmium  does  not  affect  the  bright- 
ening, but  if  the  amount  in  the  original  alloy  is  over  0.0025  per 
cent,  it  is  not  entirely  removed  by  cupelling.     In  cupelling  such 
gold,  considerable  loss  is  experienced  by  the  formation  of  volatile 
osmic  acid,  which  carries  off  so  much  gold  mechanically  that  even 
an  approximately  accurate  determination  of  the   gold  cannot   be 
made. 

Bock2  draws  the  conclusion  from  his  experiments  that  the  failure 
to  superheat  and  the  brittleness  of  silver  or  auriferous  silver  can  only 
be  attributed  to  remaining  traces  of  lead  and  bismuth.  He  confirms 
the  statement  that  the  presence  of  copper  in  cupelling  promotes 
superheating  and  also  the  malleability  of  silver  or  auriferous  silver. 
In  assaying  he  always  adds  25  grammes  of  electrically  deposited 
copper  to  500  milligrammes  of  gold,  and  by  cupelling  this  quantity 
with  3  grammes  of  lead  obtains  very  ductile  gold  buttons  which  can 
be  rolled  out  to  smooth-edged  ribbons.  This  method  originated  with 
Augendree,  it  is  used  in  the  mints  at  Brussels  and  Utrecht.3  In  as- 
saying gold  coins  or  bullion  only  0.25  gramme  is  used  and  cupelled. 
If  the  button  when  taken  from  the  muffle  does  not  brighten,  it  is 

1  Archiv.  Neerlandaises,  torn.  xv.     Bg.  u.  Huttenm.     Ztg.  1880,  p.  247. 
8  Bg.  u.  Huttenm.     Ztg.  1880,  p.  409. 
3  Dingier,  Bd.  cxix.,  p.  112. 


180  ASSAYING. 

taken  as  an  indication  of  the  presence  of  the  platinum  group  metals 
or  of  a  residue  of  lead  in  the  gold.  It  seems  to  be  a  fact  that  most 
gold  coins  as  well  as  commercial  gold  contain  an  appreciable  quan- 
tity of  the  platinum  group  metals — probably  iridosrnium.  Such 
buttons  present  an  uneven  appearance  and  the  liquid  metal  bubbles 
before  becoming  solid,  due,  in  the  presence  of  osmium,  to  osmic 
acid,  or,  in  the  presence  of  iridium  and  ruthenium,  to  oxygen. 

Samples  from  different  parts  of  the  same  piece  or  ingot  sometimes 
act  in  a  quite  different  manner  after  cupelling,  the  phenomenon  of 
brightening  occurring  in  one  and  not  in  the  other.  This  is  due 
to  the  fact  of  some  of  the  platinum  group  metals  not  being 
uniformly  distributed  or  alloyed  throughout  the  mass  of  gold.  A 
cupelled  button  of  pure  gold  which  has  been  superheated  and  shown 
brightening  can  be  hammered  and  rolled  without  cracking  the  edges. 
If  the  gold  is  not  superheated  in  cupelling,  i.  e.,  has  not  brightened, 
traces  of  lead  may  remain  in  it  which  affect  its  malleability  in  the 
same  way  as  some  of  the  platinum  group  metals. 

II.  Pulverulent  assay  (Strubprobe)  of  auriferous  silver. —  a.  A 
sample,  about  5  grammes,  is  taken  on  opposite  ends  from  the 
upper  and  lower  sides  of  a  bar.  Duplicates  of  the  sample  of  0.5 
gramme  are  weighed  out,  and  cupelled  in  the  mint  furnace  with 
8  times  the  quantity  of  silver  (p.  168)  and  the  quantity  of  lead 
which  is  found  to  be  necessary  according  to  Table  II.  p.  170,  after 
a  preliminary  assay  has  been  made.  The  resulting  button  is 
laminated  by  hammering  or  passing  it  between  rollers.  It  is  then 
placed  in  a  flask,  the  neck  of  which  should  not  be  wider  than  6 
to  8  millimeters.  Here  it  is  boiled  with  nitric  acid,  of  1.2  spe- 
cific gravity  if  the  percentage  of  gold  is  small,  and  of  1.3  specific 
gravity  if  the  percentage  is  larger,  for  instance  100  thousandths, 
until  the  vapors  of  nitrous  acid  have  disappeared.  The  bumping 
is  prevented  by  throwing  a  carbonized  grain  of  pepper,  etc.  (p. 
174)  into  the  flask.  The  pulverulent  gold  is  allowed  to  settle  in 
the  flask,  which  has  been  placed  in  a  revolving  stand.  The  acid 
is  then  poured  off  into  a  porcelain  saucer  or  cup,  and  the  gold  is 
rinsed  three  times  with  hot  distilled  water.  The  flask  is  now 
filled  with  water  and  inverted  in  a  small  unglazed  porcelain  cru- 
cible. In  this  position  it  is  placed  upon  the  revolving  stand 
until  the  gold  has  descended  into  the  crucible.  When  this  is  the 


ALLOYS  OF  GOLD.  181 

case,  the  matrass1  is  carefully  drawn  away  over  the  side  of  the 
crucible.  The  water  is  now  poured  out  of  the  crucible  by  allow- 
ing it  to  run  down  on  a  small  rod,  and  that  which  remains  behind 
is  soaked  up  with  filter-paper.  The  gold  is  then  dried  and 
strongly  ignited  in  the  crucible  so  that  the  particles  of  gold  form 
a  coherent  mass.  It  is  then  weighed. 

If  the  button  in  brightening  is  less  white,  and  does  not  "  spit," 
or  if,  as  is  the  case  where  platinum  is  present,  it  is  crystalline, 
grayish,  and  has  flat  edges,  the  gold  is  again  cupelled  with  8  times 
the  quantity  of  silver  and  3  times  that  of  lead  and  boiled  with 
acid ;  these  operations  must  be  repeated  until  the  weight  of  the 
pulverulent  gold  remains  constant. 

The  gold  may  also  be  determined  in  connection  with  Volhard's 
assay  of  silver  with  potassium  sulpho-cyanide  (p.  155).  Jiiptner2 
fuses  alloys  of  gold  and  silver  rich  in  gold,  with  5  to  8  times  the 
quantity  of  zinc,  and  dissolves  the  alloys  in  nitric  acid,  whereby 
the  gold  remains  behind. 

b.  Separation  of  auriferous  silver  grains  from  samples  of  ores. — 
This  is  done  in  the  manner  indicated  on  pp.  166  et  seq. 

B.  Alloys  of  gold  with  copper. — The  metals  are  separated  by 
cupelling  the  alloy  with  32  times  the  quantity  of  lead,  and  adding 
3  times  the  quantity  of  silver,  otherwise  the  process  is  the  same 
as  given  on  p.  170. 

Quartation  of  gold  with  cadmium.9  Balling's  method. — Cadmium 
can  advantageously  be  used  in  quartation  instead  of  silver,  as  it  is 
very  fusible,  readily  unites  with  the  gold,  and  renders  it  possible  to 
effect  the  quartation  in  a  short  time  in  a  porcelain  crucible  over  a 
lamp.  To  obtain  coherent  gold,  2J  times  its  weight  of  cadmium 
should  be  added.  The  gold-cadmium  button  is  brittle,  and  cannot 
be  flattened.  After  quartation  the  gold  retains  its  original  form, 
hut  shows  upon  its  surface  numerous  cracks  from  which  the  cad- 
mium has  been  dissolved. 

1  The  narrow  neck  of  the  flasks  used  in  the  assay  of  gold  prevents  the  air 
from  entering  while  the  flask  is  being  removed,  which  otherwise  might  stir  up 
the  gold  dust. 

2  Fresenius's  Ztschr.  1879,  p.  104;  B.  u.  h.  Ztg.  1879,  p.  187. 

3  Oestrr.  Ztschft.  f.  Bg.  u.  Httnwsn.  1879,  p.  597  ;  u.  1880,  p.  182.    Ztschft. 
f.  Anal.  Chem.,  Bd.  19,  p.  201.     Dingier,  ccxxxvi.  323. 


182  ASSAYING. 

The  gold  or  gold  alloy  is  melted  with  cadmium  under  a  flux  of 
potassium  cyanide.  After  the  fusion  is  complete,  the  crucible  is 
allowed  to  cool,  and  the  potassium  cyanide  dissolved  out  with 
water.  The  button  is  then  boiled  once  with  HN03  of  1.2  specific 
gravity,  and  twice  with  acid  of  1.3  specific  gravity,  thoroughly 
washed,  dried,  annealed,  and  weighed. 

This  method  of  quartation  offers  the  following  advantages : — 

1.  It  is  very  rapid  and  avoids  the  trouble  of  heating  up  a  muffle- 
furnace. 

2.  There  is  no  loss  of  gold  by  volatilization  or  cupellation ;  loss 
by  the  latter  means  increases  with  the  content  of  copper  in  the  gold. 

3.  The  addition  of  2J  times  as  much  cadmium  as  gold  suffices  to 
obtain  the  latter  in  a  compact  form  after  parting. 

4.  It  can  be  used  equally  as  well  with  gold-silver  alloys  as  with 
gold-copper  alloys,  and  the  separate  cupelling  of  the  gold-copper 
alloy  is  omitted. 

5.  The  thoroughly  boiled  and  washed  gold  always  shows  after 
annealing  the  pure  gold  color. 

6.  This  method  is  especially  well  adapted  for  the  immediate  assay 
of  finished  alloys. 

7.  The  content  of  silver  in  the  parting  solution  can  be  determined 
volumetrically  after  it  has  been  carefully  poured  off  from  the  gold. 

In  performing  this  assay  Kraus1  recommends  to  weigh  off  two 
separate  quantities  of  alloy  of  0.25  gramme  each.  Melt  a  piece  of 
potassium  cyanide  in  a  small  porcelain  crucible,  and  place  the  alloy 
and  cadmium  in  it.  The  fusion  takes  place  quickly ;  from  20  to 
30  fusions  may  be  made  in  an  hour  by  using  several  crucibles  and 
dissolving  out  the  potassium  cyanide  as  soon  as  the  fusion  is  com- 
plete. The  buttons  should  be  boiled  in  HN03  of  1.3  specific  gravity 
for  not  less  than  half  an  hour ;  or  longer,  according  to  the  amount 
of  gold  present.  Boil  a  second  time  10  minutes  in  acid  of  same 
strength  and  a  third  time  in  water  5  minutes. 

As  it  can  be  quickly  executed,  Yolhard's  method  is  the  most  con- 
venient for  the  determination  of  the  silver  in  the  solutions  poured 
off  from  the  quartation.  Of  course,  the  wash-water  as  well  as  the 
nitric  acid  solutions  must  be  so  titrated  after  cooling. 

Juptner's2  volumetric  assay  of  gold. — If  the  gold  alloys  to  be 
assayed  contain  tin,  antimony,  or  some  platinum  metals,  all  of 

*  Dingier,  ccxxxvi.  323. 

2  Oestrr.  Ztschft.  f.  Bg.  u.  Httnwsn.  1880,  p.  182. 


ALLOYS   OF   GOLD.  183 

which  are  insoluble  in  HN03,  such  insoluble  residues  are  treated 
with  HC1  +  HN03.  The  platinum  metals  are  precipitated  with 
ammonium  chloride,  evaporated  to  dryness,  taken  up  with  water 
and  filtered  off.  Mix  the  filtrate  with  a  measured  excess  of  the 
ferrous  sulphate,  reducing  the  chloride  to  metallic  gold,  then  titrate 
the  non-oxidized  portion  of  the  ferrous  oxide  with  permanganate. 
The  reaction  is  expressed  by  the  following  equation — 

Au203  +  6FeO  =  2Au  +  3Fe2Os 
More  correctly  2AuCl3  +  6FeS04  =  2Au  +  Fe2Cl6  4-  2[Fe2(S04)3]. 

Hence,  2  gold  correspond  to  6  iron,  or  1  gold  to  3  iron ;  designa- 
ting the  portion  of'iron  oxidized  in  titrating  with  permanganate  by 
m,  and  the  content  of  gold  sought  by  x,  we  havre  the  proportion — 

3  Fe  :  An  =  168  :  196.7  =  m  :  x 

196.7 

x=    1£iu  ,  m  =  1.172  m. 
loo 

Preparation  of  the  ferrous  ammonium  sulphate  solution. — Dis- 
solve 6  grammes  of  Mohr's  salt  in  one  liter  of  water  acidulated 
with  H2S04.  These  6  grammes  contain  6  X  0.14285  =  0.857 
gramme  of  iron,  and  1  c.c.  of  this  solution  precipitates  exactly  one 
milligramme  of  gold. 

Preparation  of  the  permanganate  solution. —  This  solution  should 
be  so  prepared  that  1  c.c.  will  exactly  correspond  to  1  c.c.  of  Mohr's 
salt  solution.  It  is  then  only  necessary  to  deduct  the  number  of 
c.c.  of  permanganate  used  in  titrating  from  the  amount  of  ferrous 
ammonium  sulphate  solution  added  to  the  gold  solution,  in  order  to 
determine  the  amount  of  gold,  in  milligrammes,  in  the  solution  of 
the  alloy. 

Separation  of  gold  from  platinum  by  electrolysis.1 — By  bring- 
ing gold  in  connection  with  the  positive  pole  of  a  battery  in  a  bath 
of  chloride  of  gold,  it  dissolves  and  firmly  deposits  itself  on  the 
negative  electrode  without  the  bath  undergoing  any  change.  The 
gold  to  be  so  treated  should  be  in  the  form  of  a  sheet  and  connected 
to  the  positive  pole  by  means  of  a  copper  wire.  An  accurately 
weighed  sheet  of  the  purest  gold  should  be  connected  with  the 
negative  pole.  Both  sheets  are  placed  in  the  solution  of  chloride  of 
gold  and  subjected  to  the  action  of  the  electric  current.  The  gold 
disappears  from  the  positive  pole  and  is  deposited  on  the  negative 

1  Fortschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  116. 


184  ASSAYING. 

pole,  while  the  platinum  metals  are  liberated  and  fall  to  the  bottom 
as  a  gray-black  powder.  When  all  the  gold  has  been  deposited,  the 
sheet  of  gold  at  the  negative  pole  is  washed  with  water  and  alcohol, 
dried,  and  weighed.  The  increase  in  weight  equals  the  amount  of 
pure  gold  in  the  alloy.  This  method  is  used  on  a  large  scale  for 
the  production  of  tine  gold  in  the  North  German  refining  works  at 
Hamburg.1 

Toughening  brittle  gold. — This  is  sometimes  necessary  when  the 
metal  has  been  rendered  brittle  by  the  presence  of  minute  quanti- 
ties of  other  metals  or  impurities. 

Roberts'2  removes  such  impurities  by  converting  them  into  vola- 
tile chlorides  by  a  stream  of  chlorine  gas. 

According  to  Wagner,3  bromine  may  be  used  instead  of  chlorine 
for  this  purpose.  Brittle  gold  may  also  be  toughened  by  throwing 
a  small  quantity  of  corrosive  sublimate  (mercuric  chloride)  on  the 
surface  of  the  molten  metal. 

It  can,  according  to  Warington,4  be  toughened  by  the  addition 
of  about  10  per  cent,  of  black  oxide  of  copper.  If  the  gold  is  but 
slightly  brittle,  it  may  be  toughened  by  simply  pouring  it  in  a  thin 
stream  through  atmospheric  air  into  a  crucible  lined  with  borax,  or 
by  the  addition  of  a  small  amount  of  chloride  of  copper.5 

Booth6  uses  a  flux  of  soda-ash  and  borax  glass.  When  a  quiet 
fusion  has  taken  place  a  small  quantity  of  nitre  is  added.  The 
moment  that  the  visible  oxidizing  action  begins  to  slacken,  the  flux 
is  skimmed  off.  The  gold  in  the  pot  will  then  be  found  toughened. 


V,  PLATINUM, 

36.    ORES. 

Native  platinum  is  almost  always  combined  with  other  metals  of 
the  platinum  group  (Rh,  Ir,  Pd,  Os),  with  precious  (Au)  and  base 

1  Bg.  u.  h.  Ztg.,  1880,  p.  411. 

2  First  and  Second  Annual  Reports  of  Deputy-Master  of  Mint,  1870-72, 
.pp.  93  and  34,  respectively.     See  Percy's  Metallurgy,  Silver  and  Gold,  pp.  405, 
407,  and  437. 

3  Bull.  Chera.  Soc.,  Paris,  t.  xxv.  1876,  p.  138. 

4  Journ.  Chem.  Soc.,  xiii.  1860,  p.  31. 

6  Encyclopaedia  Britannica,  vol.  x.  p.  750. 

6  Engineering  and  Mining  Journ.,  July  12,  1884,  p.  22. 


ASSAY  OF   PLATTNIFEROUS   ORES.  185 

metals   (Fe,   Cu),   and   admixed   with   iridosmium,  earthy  and 
metallic  minerals. 


37.    ASSAY   OF   PLATINIFEROUS   ORES. 

A.  Fire  assays.1 — These  extend  to  the  determination  of — 

1.  Percentage  of  sand. — 2  grammes  of  ore  are  mixed  with  10 
grammes  of  granulated  silver  and  placed  in  a  clay  crucible  glazed 
with  fused  borax.     It  is  covered  with  10  grammes  of  borax  glass, 
with  a  small  piece  of  wood  charcoal,  and  fused.     The  resulting 
button  is  weighed,  and  its  difference  in  weight,  as  compared  with 
that  of  the  ore,  giving  due  consideration  to  the  added  silver,  in- 
dicates the  percentage  of  sand. 

2.  Percentage  of  gold. — 10  grammes  of  the  ore  are  boiled  with 
mercury  for  several  hours.     It  is  then  washed  out  with  hot  mer- 
cury, and  the  gold  amalgam  distilled  in  a  small  retort. 

3.  Percentage  of  platinum. — The  platinum  is  combined  with 
lead  by  fusing  50  grammes  of  ore  with  75  grammes  of  granu- 
lated lead,  50  grammes  of  galena,  10  to  15  grammes  of  borax, 
and  adding  to  the  fused  mass  50  grammes  of  litharge;   or  20 
grammes  of  ore  are  fused  with  15  grammes  of  borax,  30  grammes 
of  soda,  1  gramme  of  powdered  charcoal,  and  50  grammes  of 
litharge.     The  fused  mass  is  allowed  to  cool  off,  and  the  lead 
button  separated  from  the  matt  (sulphur  compounds  of  copper, 
iron,  and  lead)  above  it,  and  the  iridosmium  below  it.     The  lead 
button,  if  too  large,  is  scorified  with  some  borax  (p.  64),  and 
cupelled  at  as  high  a  temperature  as  possible.2     The   platinum 
remaining  is  purified  by  a  further  fusion  with  6  to  7  per  cent,  of 
lead  in  a  lime  crucible  heated  with  illuminating  gas  and  oxygen.8 

B.  Wet  assay. — 5  to  10  grammes  of  ore  are  treated  with  hydro- 
chloric acid,  and  the  residue  is  washed  out  and  digested  with  aqua 
regia  for  from  8  to  12  hours.     The  platiniferous  solution  is  filtered 
from  the  residue  (sand,  iridosmium)  and  evaporated  almost  to 
dryness.     Absolute  alcohol  and  solution  of  sal-ammoniac  are  then 

1  Mispratt's  Chem.,  v.  1151. 

2  [The  surface  of  the  button  after  this  operation  is  dull  and  the  fracture 
crystalline,  even  when  very  small  quantities  of  platinum  are  present. — G.] 

3  [The  amount  of  lead  retained  in  the  unpurified  button  varies  from  ^  to  ^  of 
its  weight.— G.] 


186  ASSAYING. 

added  until  a  precipitate  ceases  to  form.  This  is  again  filtered 
and  washed,  and  the  yellow  ammonio-platinic  chloride  is  dried. 
This  is  highly  heated,  and  the  resulting  spongy  platinum  weighed. 
If  the  ore  contains  gold,  it  is  precipitated  from  the  filtrate  of 
ammonio-platinic  chloride  with  ferrous  sulphate.  The  precipitated 
gold  is  then  digested  with  hydrochloric  acid,  filtered,  washed,  and 
dried,  and  fused  with  the  addition  of  some  borax  glass. 

38.    ALLOYS   OF   PLATINUM. 

These  may  be  : — 

1.  Gold  with  platinum. — The  alloy  is  cupelled  with  three  times 
the  quantity  of  silver,  and  sufficient  lead  to  remove  any  copper 
which  may  be  present  (8  to  30  times  the  quantity  of  lead  if  from 
200  to  500  thousandths  or  more  of  copper  are  present.)     The 
laminated  button  is  treated  with  nitric  acid,  as  in  the  gold  assay 
(p.  170),  whereby  the  platinum  will  be  dissolved  with  the  silver, 
the  gold  remaining  behind.     The  silver  is  precipitated  from  the 
solution  by  means  of  common  salt,  and  the  platinum  is  separated 
from  the  filtrate  as  ammonio-platinic  chloride,  and  further  treated 
as  on  p.  185.     If  the  percentage  of  gold  is  large,  the  alloy  is 
dissolved  in  aqua  regia,  and  the  separation  conducted  in  the  man- 
ner indicated  for  platinum  ores  (p.  185). 

2.  Silver  with  platinum. — 0.5  gramme  of  the  alloy  is  cupelled 
with  a  sufficient  quantity  of  lead  to  remove  the  copper  which 
may  be  present,  and  with  such  a  quantity  of  silver  (to  be  deter- 
mined by  a  preliminary  assay)  as  to  make  the  ratio  1  part  plati- 
num to  2  parts  of  silver.    The  alloy  is  laminated  and  boiled  twice 
(each  time  from  10  to  12  minutes)  with  concentrated  sulphuric 
acid  of  1.85  specific  gravity,  whereby  platinum  will  remain  be- 
hind in  the  form  of  a  small  roll,  and,  if  a  larger  quantity  of 
silver  is  present,  as  a  powder.     It  is  then  washed  with,  hot  water, 
dried,  ignited,  and  weighed. 

3.  Silver  and  gold  with  platinum. — 200  milligrammes  are  cu- 
pelled with  sufficient  silver,  for  instance,   100  milligrammes,  to 
make  the  ratio  1  part  gold  to  3  parts  silver,  and  with  lead  to  re- 
move the  base  metals.     The  button  is  laminated,  being  frequently 
heated  during  the  operation.     It  is  then  made  into  a  roll  and 
boiled  with  concentrated  sulphuric  acid.     The  residue  is  washed, 


NICKEL ORES.  187 

ignited,  and  weighed;  the  difference  in  weight  represents  the 
.v//nr  originally  present  plus  that  added  to  it.  The  residue,  con- 
taining gold,  platinum,  and  iridosmium,  is  cupelled  with  lead, 
and  with  a  quantity  of  silver  at  least  12  times  that  of  the  plati- 
num (the  effect  of  less  silver  would  be  to  leave  a  residue  of  plati- 
num, and  if  more  is  taken  the  residue  will  be  pulverulent  instead 
of  in  the  form  of  a  roll).  The  roll  is  first  boiled  with  nitric  acid 
of  1.16  specific  gravity,  and  then  with  acid  of  1.26  specific 
gravity,  after  which  the  residuum  (gold  and  iridosmium)  is 
washed  and  ignited.  The  dissolved  platinum  is  determined  from 
the  difference.  The  residue  is  digested  writh  aqua  regia,  and  the 
gold  precipitated  with  ferrous  sulphate,  while  iridosmium  remains 
behind.  About  3  hours  are  required  for  two  assays. 

Electrolytic  assay.1 — Compounds  of  platinum  are  decomposed 
with  the  greatest  ease  by  the  galvanic  current,  with  the  deposition 
of  the  metal  on  the  negative  electrode.  A  current  of  two  Bunsen 
cells  produces  decomposition  so  rapidly  that  the  platinum  separates 
as  platinum  black,  and  cannot  be  determined.  If  one  cell  is  used 
it  separates  in  so  dense  a  form  that  it  cannot  be  separated  from 
hammered  platinum.  "It  is  possible,  in  this  way,  to  gradually  de- 
posit considerable  quantities  of  platinum  on  the  negative  electrode 
without  changing  its  appearance.  For  the  determination  of  plati- 
num in  its  salts,  the  solution  may  be  slightly  acidified  with  HC1  or 
H2S04,  or  treated  with  ammonium  or  potassium  oxalate,  gently 
warmed  and  electrolyzed.  The  platinum  separates  in  a  compara- 
tively short  time ;  for  example,  a  solution  of  platinum  chloride  di- 
luted to  200  c.c.,  containing  0.6  gramme  platinum,  deposited  0.5 
gramme  in  five  hours. 

Iridium  is  not  reduced  from  its  solutions  by  a  single  Bunsen 
cell;  this  fact  may  be  used  for  the  separation  of  platinum  from 
iridiuin. 

VI,  NICKEL, 

39.    ORES. 

Copper  nickel,  NiAs,  with  44  Ni ;  antimonial  nickel  (breithaup- 
tite),  NiSb,  with  31.4  Ni ;  rammelsbergite,  NiAs,,,  with  28.2  Ni; 

1  Classen's  Chem.  Analysis  by  Electrolysis.  [Trans.]  New  York.  1887. 
p.  71. 


188  ASSAYING. 

nickel  sulphide  (millerite),  NiS,  with  64.5  Ni ;  antimonial  nickel  ore 
(ullmannite),  NiSbS,  with  27.6  Ni;  nickel  glance  (gersdorffite), 
NiAsS,  with  35.1  Ni;  nickel  silicates  as  revdanskite  and  garnierite, 
with  10  to  20  Ni;  nickel  arseniate,  Ni3As2O8 + 8H2O,  with  29.5 
Ni ;  nickeliferous  iron,  copper,  and  magnetic  pyrites. 

40.  FIRE  ASSAY  (Plattner's  Assay). 

This  is  based  upon  the  formation  of  constant  combinations  of 
Ni2As,  and  Co2As,  with  respectively  60.7  Ni  and  61.1  Co,  and 
their  subsequent  treatment,  in  a  manner  to  be  indicated  with 
borax,  after  other  foreign  admixtures  have  been  removed.  The 
process  requires  certain  modifications  if  copper,  lead,  bismuth,  and 
antimony  are  present. 

A.   Compounds  free  from  copper. 

1.  A  sufficient  quantity  of  assay  sample  is  weighed  out  so  that 
the  resulting  buttons  of  Ni2As  and  Co2As  will  weigh  from  0.4  to 
0.6  gramme.     Thus,  about  5  grammes  of  poor  ores  will  be  re- 
quired, 1.5  to  2.5  grammes  of  medium,  and  0.5  to  0.6  gramme  of 
rich  ores. 

2.  Compounds  containing  metallic  sulphides  must  be  completely 
roasted  with  charcoal  and  ammonium  carbonate  ;  otherwise,  the 
buttons  cannot  be  properly  slagged  with  borax.     Substances  free 
from  sulphur  need  not  to  be  roasted. 

Five  grammes  of  ore  containing  sulphates  which  cannot  be  de- 
composed by  roasting  (gypsum,  barytes,  etc.),  with  10  to  15 
grammes  of  borax,  5  to  10  grammes  of  glass,  and  0.5  gramme  of 
resin  are  placed  in  a  suitable  crucible  (Fig.  52,  p.  65),  covered 
,with  a  layer  of  common  salt,  and  fused  to  (brittle)  matt  (p.  99). 
This  is  dead-roasted.  0.5  to  1.5  grammes  of  arsenic  are  added  if 
the  nickel  was  not  combined  with  sulphur  or  arsenic. 

3.  Arsenizing. — The  roasted  assay  sample  is  intimately  rubbed 
together  with  1  to  1J  times  the  quantity  of  metallic  arsenic  in  an 
iron  mortar,  placed  in  a  suitable  covered  crucible  (Fig.  52,  p.  65), 
and  heated  in  the  muffle,  kept  at  orange-red  heat  (for  10  to  15 
minutes)  until  the  arsenical  flame  and  vapors  have  ceased  to  ap- 
pear.    When  this  is  the  case,  the  metallic  oxides  contained  in  the 
roasted  sample  will  have  been  reduced  by  a  part  of  the  arsenic, 


NICKEL — FIRE   ASSAY.  189 

and  converted  by  another  part  into  metallic  arsenides  of  variable 
composition  (of  iron,  nickel,  cobalt,  etc.),  which  are  either  only 
sintered  together  (especially  if  the  charge  is  rich  in  cobalt),  or 
fused. 

Compounds  free  from  sulphur  and  rich  in  arsenic,  containing 
more  arsenic  than  is  necessary  for  the  formation  of  Co2As  and 
Ni8As,  do  not  require  roasting  and  arsenizing.  Alloys  (argentan, 
nickel  coins,  nickeliferous  black  copper,  etc.)  must  be  laminated, 
and  several  times  arsenized  with  an  equal  quantity  of  arsenic ; 
and  also  substances  rich  in  cobalt  (for  instance,  mixtures  of  nickel 
and  cobalt  oxides),  which  may  have  been  precipitated  in  the  wet 
way. 

4.  Reducing  and  solvent  fusion  for  the  purpose  of  collecting  the 
metallic  arsenides  into  a  button  (arsenical  iron,  arsenical  nickel, 
arsenical  cobalt),  and  of  slagging  off  earths  and  foreign  oxides, 
zinc  being  entirely,  and  antimony  partly  volatilized  in  the  opera- 
tion. The  mass  is  placed  in  a  sound  crucible,  and  10  to  12.5 
grammes  of  potassium  carbonate  and  flour  are  added  to  it.  Upon 
this  is  placed  one  small  spoonful  of  borax  and  two  of  powdered 
glass,  and  a  covering  of  common  salt  with  a  small  piece  of  coal. 
The  crucible  is  then  placed  in  the  muffle-furnace,  wood-charcoal 
is  piled  high  around  it,  the  mouth  of  the  muffle  is  closed,  and  the 
charge,  after  the  "  flaming"  has  ceased,  is  fused  for  one-half  to 
three-quarters  of  an  hour  at  an  orange-red  heat.  The  assay  is 
then  taken  out,  allowed  to  cool  off,  and  the  brittle  button  very 
carefully  freed  from  slag. 

Modifications  which  may  occur. 

a.  Addition  of  iron  filings  :  0.5  to  0.75  gramme  of  iron  filings 
must  be  added  during  arsenizing,  if  the  ores,  etc.,  are  rich  in 
cobalt,  and  refractory ;  0.05  to  0.20  gramme,  if  they  are  entirely 
free  from  iron,  or  contain  but  little  of  it,  in  order  to  prevent  the 
slagging  off  of  cobalt  too  soon,  by  the  borax.  If  lead  is  present, 
0.5  to  0.75  gramme  of  iron  in  the  form  of  a  thick  wire  is  added, 
or  the  mass  is  fused  in  an  iron  crucible,  which  will  allow  a  better 
regulation  of  the  consumption  of  iron.  The  lead  attaches  itself 
upon  the  button  of  arsenides,  and  its  weight  is  found  by  weighing 
lead  and  button  together,  cutting  the  former  off  and  reweighing. 
If  bismuth  is  present,  it  will  attach  itself  upon  the  brittle  but- 


190  ASSAYING. 

ton  of  arsenides,  in  the  form  of  brittle  metal,  which  cannot  be 
detached  from  it.  In  this  case,  it  is  necessary  to  add  0.5  to  0.6 
gramme  of  granulated  lead  to  the  charge,  when  a  ductile  alloy  of 
both  metals  will  separate  on  the  button  of  arsenides,  which  can 
be  easily  disconnected  from  it.  The  approximate  percentage  of 
bismuth  can  be  calculated  after  deducting  the  added  granulated 
lead,  minus  4  per  cent.  loss. 

b.  Arsenizing  and  fusion  in  one  operation. — The  roasted  assay 
sample  is  rubbed  together  with  arsenic  in  the  same  manner  as 
previously  stated,  and  the  mixture  is  wrapped  up  in  a  cylinder  of 
soda  paper.  The  cylinder  is  formed  over  a  wooden  stick  of  16 
millimeters  diameter,  by  closing  the  lapping  edges  with  lac.  It  is 
pressed  firmly  into  a  crucible  (Fig.  52,  p.  65)  and  covered  with  15 
grammes  of  black  flux,  1  small  spoonful  of  borax,  1  small  spoonful 
of  glass,  15  grammes  of  common  salt,  and  a  small  piece  of  charcoal. 
Accurate  results  are  obtained  by  this  process. — Or,  the  roasted 
sample  is  rubbed  together  with  an  equal  quantity  of  arsenic  and 
15  per  cent,  of  arsenical  iron  (Fe2As),  and  fused  with  the  above 
fluxes. 

5.  Slagging  off  of  the  arsenical  iron. — Wood  charcoal  is  placed 
all  about  the  inside  of  the  muffle,  and  one  or  two  refining  dishes 
are  placed  in  the  centre  of  it.  The  muffle  is  then  closed,  and 
the  dishes  are  brought  to  a  white  heat  by  a  strong  fire.  1.5  to  2 
grammes  of  borax  glass  are  then  placed  in  the  dishes  by  means  of 
an  iron  spoon  (or  wrapped  up  in  a  cornet),  the  muffle  is  closed  and 
the  borax  fused.  The  button  of  arsenides  is  now  placed  in  the 
dish,  the  mouth  of  the  muffle  is  again  closed,  and  the  button 
fused  as  quickly  as  possible  at  a  very  high  temperature  (if  the 
temperature  is  too  low  and  the  fusing  takes  too  much  time, 
obalt  also  will  be  slagged  off ).  The  mouth  of  the  muffle  is  now 
opened,  placing  a  piece  of  glowing  charcoal  in  front,  to  allow  the 
entrance  of  air,  whereby  the  arsenide  of  iron  is  oxidixed  to  basic 
iron  arseniate.  This  covers  the  button  with  a  crust  or  scale  (the 
scaling  of  the  button)  which  is  continuously  dissolved  by  the 
borax  until  the  surface  of  the  dull  button  appears  bright,  when 
this  operation  is  finished.  The  dish  is  lifted  out  by  means  of  the 
tongs,  and  the  lower  part  of  it  is  first  dipped  into  water  until  its 
contents  have  ceased  to  glow,  when  the  entire  dish  is  submerged. 


NICKEL — FIRE  ASSAY.  191 

The  following  are  indications  of  a  successful  assay :  The  button 
is  bright,  the  slag  black  or  green,  with  a  bluish  tint,  which  is  a 
sure  indication  of  all  the  iron  having  been  removed. 

Modifications. — If  the  button  is  very  rich  in  iron  it  is  repeat- 
edly treated  with  fresh  borax,  as  this  is  saturated  and  becomes  stiff 
and  the  button  no  longer  "  drives." 

Separation  of  copper-red  scales  of  iron  arseniate  from  strongly 
saturated  borax.  More  cobalt  will  slag  off  (the  slag  has  a  strong 
blue  tint)  if  the  temperature  is  too  low  or  the  slagging  off  is 
continued  too  long,  or  when  no  iron,  or  but  little  of  it,  was 
present  in  the  button. 

6.  Dearsenizing. — An  excess  of  arsenic  is  volatilized  by  heating 
the  button  in  a  small  covered  crucible  (Fig.  49,  p.  64)  in  charcoal 
powder,  in  the  muffle  heated  to  bright  redness  for  one- fourth  to 
one-half  hour,  in  order  that  constant  combinations  of  Ni2As  and 
Co2As  shall  be  formed.     The  resulting  button  is  weighed,  and 
the  operation  is  repeated  until  its  weight  remains  constant. 

7.  Slagging  off  the  cobalt  arsenide. — The  process  is  the  same  as 
in  slagging  off  the  iron  arsenide  (p.  190),  but  at  a  higher  temper- 
ature, the  quiet  button  remaining  bright  during  the  slagging  off 
of  the  cobalt.     The  process  is  interrupted  as  soon  as  a  film  of 
apple-green  basic  nickel  arseniate  forms  on  the  surface  of  the 
button.     The  dish  is  taken  and  cooled  off  in  the  same  manner 
as  in  the  slagging  off  of  iron  arsenide  (p.  190).     If  the  assay 
has  been  properly  done,  the  bright,  white  button  will  show  on  its 
surface  small  green  patches  of  nickel  arseniate,  the  slag  is  blue 
with  a  violet  tint  (from  the  blue  of  the  cobalt  and  the  brown  of 
the  nickel),  and  a  green  stain  will  be  perceptible  on  the  place 
where  the  button  has  rested.     The  button  consisting  of  Ni2As  is 
weighed,   and    the    percentage   of  nickel   calculated   therefrom 
(p.  188),  the   Co2As   being  determined  from   the  difference  of 
Co2As  -f  Ni2As2. 

B.   Cupriferous  compounds. 

A  percentage  of  copper1  remains  behind  with  NiaAs  as  a  con- 
stant combination  of  Cu3As,  and  can  be  determined  according 
to  Plattner's  method  : 

1  B.  u.  h.  Ztg.  1868,  p.  24 ;  1868,  p.  94  (Kleinschmidt) ;  1878,  p.  88 
(Schweder). 


OF  THE 

UNIVERSITY  H 


192  ASSAYING. 

1.  If  the  percentage  of  copper  is  small,  and  does  not  exceed 
that  of  nickel,  by  the  addition  to  the  weighed  button  (Ni2As  4-' 
Cu3As)  of  6  to  8  times  the  quantity  of  gold  accurately  weighed 
(to  prevent  a  slagging  off  of  the  copper  in  the  subsequent  opera- 
tion).    The  arsenide  button  with  gold  addition  wrapped  in  a 
cornet  is  placed  in  salt  of  phosphorus  which  has  been  fused  in  a 
suitable  shallow  dish.     This  salt  exerts  a  more  vigorous  effect 
than  borax  in  slagging  off  with  yellowish-brown  color  the  nickel 
arseniate  which  will  be  formed.     If  necessary,  the  oxidizing  pro- 
cess is  continued  by  renewing  the  saturated  salt  of  phosphorus 
until  the  button  appears  bright,  a  proof  that  the  nickel  is  slagged 
off,  the  complete  volatilization  of  the  arsenic  being  indicated 
later  on  by  the  button  ceasing  to  fume.     The  remaining  alloy  of 
Au  and  Cu  is  weighed,  and  the  weight  of  the  copper,  which  is 
obtained  by  deducting  that  of  the  added  gold,  is  calculated  to 
Cu3As,  with    71.7  per  cent.  Cu,  and   deducted  from   the  total 
weight  of  the  Ni2As  +  Cu3As,   from   which  the  percentage  of 
nickel  is  calculated. 

This  assay  becomes  less  accurate  with  an  increase  in  the  per- 
centage of  copper,  as,  during  the  slagging  off  of  the  last  portions 
of  the  nickel  arseniate,  the  copper  also  commences  to  slag  off. 
For  this  reason — 

2.  The  wet  method  is  partially  made  use  of  when  the  percent- 
age of  copper  is  large.     The  processes  are  as  follows : — 

a.  The  button  consisting  of  Ni2As  and  Cu3As  is  dissolved  in 
nitric  acid,  and  evaporated  to  dryness  with  sulphuric  acid.     The 
residue  is  digested  with  aqueous  sulphurous  acid  until  no  odor  of 
the  latter  remains.     The  copper  and  arsenic  (also  antimony)  are 
now  precipitated  from  acid  solution  by  sulphuretted  hydrogen, 
and  the  arsenic  sulphide  (also  antimony  sulphide)  is  extracted 
with  a  warm  solution  of  sodium  sulphide.     The  residue  remain- 
ing in  the  filter  is  washed  and  dried  in  the  roasting  dish  in  front 
of  the  muffle,  and  is  then  ignited.    The  copper  sulphide  is  rubbed 
up    and   strongly    heated,    ammonium    carbonate    being    added 
towards  the  end.     The  copper  oxide  which  has  been  produced  is 
weighed,    and   calculated   to   Cu3As.      This   is   deducted    from 
Ni2As  4-  Cu3As  to  determine  the  NiaA.s  (Patera). 

b.  By  another  method,  the  ore,  etc.,  is  dissolved,  and  the  copper 


NICKEL — FIRE   ASSAY.  193 

precipitated  by  the  galvanic  current  (pp.  110  et  seq.\  and  the 
remaining  solution  with  potassium  hydrate.  The  precipitate, 
containing  iron,  nickel,  and  cobalt,  is  washed,  dried,  ignited,  arse- 
nized,  and  the  further  process  conducted  as  given  in  the  dry 
method,  p.  188.  When  much  iron  is  present,  it  is  better,  on 
account  of  the  labor  of  washing  the  iron  precipitate,  to  prepare 
an  assay  according  to  Plattner,  for  Ni2As  -f  Cu3As,  to  separate 
the  copper  from  a  second  fresh  charge  by  electrolysis,  to  calculate 
the  copper  to  Cu3As,  and  deduct  this  from  Ni2As  +  Cu3As,  which 
will  give  the  Ni,As  (Schweder). 

Nickeliferous  pyrrhotine,  with  0.82  per  cent.  Cu  and  1.72  per 
cent  Ki  and  Co  :  2  grammes  are  dissolved  as  above,  p.  Ill,  and 
the  copper  is  precipitated  by  electrolysis  from  a  solution  of  40 
cubic  centimeters  of  nitric  acid,  and  360  cubic  centimeters  of 
water  (p.  110);  or  5  grammes  of  ore  are  roasted  and  charged 
with  arsenic  in  a  soda  paper  cylinder  (p.  190),  anfl  fused  with 
mixing  agents  in  the  crucible  (p.  191);  the  iron  is  slagged  off 
twice  and  the  button  then  dearsenized.  If  cobalt  is  absent, 
Ni2As  -f  Cu3As  will  remain  behind,  and  the  nickel  is  then  calcu- 
lated as  previously  stated  (p.  191).  Cobalt  and  nickel  may  also 
be  determined  by  electrolysis,  and  calculated  to  (Ni,Co)2As  and 
the  Cu2As  determined  from  the  difference. 

c.  Compounds  soluble  with  difficulty,  as,  for  instance,  slags. — These 
are  roasted,  arsenized,  and  fused  according  to  the  process  given 
on  p.  188.  If  they  are  poor  in  nickel,  several  buttons  (say  five) 
are  wrapped  in  a  cornet  and  treated  with  borax,  as  before  de- 
scribed. The  iron  is  slagged  off,  the  excess  of  arsenic  removed, 
and  the  button  (Ni2As  +  Cu3As)  weighed.  It  is  then  dissolved  in 
20  cubic  centimeters  of  nitric  acid,  200  cubic  centimeters  of  water 
are  added,  and  the  copper  is  precipitated  by  electrolysis  until  it 
commences  to  be  colored  black  by  the  arsenic  (p.  112).  The 
Cu3As  is  calculated  from  the  precipitated  copper,  and  deducted 
from  the  Ni2As  +  Cu3As,  etc.,  or,  what  is  still  better,  in  order  to 
avoid  constantly  watching  the  precipitation  of  copper,  lest  arsenic 
be  precipitated  with  it,  the  button  of  Ni2 As  -f  Cu3As  is  dissolved 
in  nitric  acid,  in  a  covered  beaker-glass,  then  evaporated  to  dry- 
ness,  and  the  copper  and  arsenic  are  precipitated  with  sulphuret- 
ted hydrogen.  The  filtrate  is  heated  in  order  to  drive  off  the 
13 


194  ASSAYING. 

sulphuretted  hydrogen,  ammonium  sulphate  and  ammonia  are 
added,  and  the  nickel  determined  by  electrolysis  (see  later  on). 
This  is  calculated  to  Ni2As,  which  is  deducted  from  NiAs-f- 
Cu3As  and  Cu3As  is  found  from  the  difference. 

C.   Compounds  containing  antimony. 

If  a  large  amount  of  antimony  is  present,  it  becomes  necessary 
to  remove  it  from  the  dissolved  ore  by  sulphuretted  hydrogen. 
It  is  then  filtered,  and  the  filtrate  boiled  in  order  to  expel  the 
sulphuretted  hydrogen.  The  filtrate  is  now  oxidized  with  potas- 
sium chlorate,  the  iron,  nickel,  and  cobalt  are  precipitated  with 
potassium  hydrate,  and  the  precipitate  is  filtered,  dried,  ignited, 
and  arsenized  (p.  188). 

41.    WET  ASSAY. 

The  gravimetric  analysis,  being  more  accurate,  and,  especially 
the  electrolytic  assay,  more  simple  than  the  volumetric  analysis,  it 
is  more  frequently  used  for  the  wet  assay  of  nickel. 

A.   Gravimetric  assay. 

«7 

1.  Electrolytic  assay.1 — This  is  based  upon  the  precipitation  of 
nickel  (and  at  the  same  time  of  cobalt,  if  present)  from  ammoni- 
acal  solution  (copper  from  acid  solution)  by  the  galvanic  current. 
When  copper  and  lead  are  present,  1  gramme  of  ore  is  dissolved 
in  20  cubic  centimeters  of  nitric  acid,  and  evaporated  with  a  few 
drops  of  sulphuric  acid  in  order  to  form  lead  sulphate,  and  the 
copper,  antimony,  and  arsenic  in  acid  solution  are  precipitated 
with  sulphuretted  hydrogen.  (This  method  of  precipitation  is  to 
be  preferred,  as,  if  the  copper  is  previously  precipitated  from  acid 
solution  by  the  galvanic  current,  antimony  and  arsenic  remain  in 
the  filtrate.) 

The  filtrate  is  evaporated  in  a  porcelain  dish,  first  over  the 
lamp,  then  on  the  water-bath,  with  the  addition  of  a  few  drops  of 
nitric  acid  ;  and,  in  case  dust  should  float  in  the  fluid,  some  hy- 
drochlorate  acid  is  also  added,  when  the  liberated  chlorine  will 
destroy  the  organic  substances  which  otherwise,  being  converted 
into  sugar  by  sulphuric  acid,  would,  in  the  subsequent  precipita- 

1  Fresenius's  Ztschr.  1872,  p.  1 ;  B.  u.  h.  Ztg.  1877,  p.  5  (Schweder). 


NICKEL — WET   ASSAY.  195 

tion  of  the  iron,  hold  a  part  of  it  in  solution  as  ferrous  oxide, 
which  would  then  be  precipitated  with  the  nickel.  The  free  sul- 
phuric acid  is  expelled  by  heating  the  sand-bath.  The  mass  is 
next  dissolved  in  water  and  supersaturated  with  ammonia,  in 
order  to  prepare  an  ammoniacal  solution  of  copper. 

If  but  little  iron  is  present,  ammonia  may  be  used  directly ;  but 
should  there  be  a  larger  quantity,  the  precipitated  ferric  hydrate 
remains  nickeliferous.  If  this  is  the  case,  the  residue  completely 
freed  from  free  sulphuric  acid  by  evaporation,  is  dissolved  in  100 
cubic  centimeters  of  hot  wrater,  and  after  the  solution  has  become 
entirely  cold,  200  to  300  cubic  centimeters  of  cold  water  are 
added,  according  as  more  or  less  iron  is  present.  Next  a  solution 
of  ammonium  sesquicarbonate  in  12  parts  of  water  is  added  drop 
by  drop  from  a  pipette,  under  constant  stirring,  until  the  liquid 
appears  dark  brown,  but  without  being  turbid  (if  this  is  the  case,  a 
few  drops  of  sulphuric  acid  must  be  added),  and  without  developing 
carbonic  acid.  The  vessel  is  then  covered  with  a  watch-crystal, 
and  the  liquid  slowly  heated  to  the  boiling  point,  whereby  the 
greatest  part  of  the  iron  will  be  separated  as  basic  sulphate  of  a 
leather-yellow  color.  The  vessel  is  taken  from  the  fire,  the 
watch-crystal  rinsed  off,  and  the  liquid  placed  in  the  water-bath 
and  allowed  to  settle.  It  is  then  filtered,  and  the  precipitate, 
which  is  free  from  cobalt  and  nickel,  washed  with  hot  water.  If 
the  assay  sample  is  rich  in  iron,  the  filtrate  will  still  contain  Fe. 
In  this  case  it  is  allowed  to  become  quite  cold,  and  is  then  again 
precipitated  with  ammonium  carbonate,  as  above,  etc.,  but  the 
filtrate  will  always  contain  notable  traces  of  iron.  A  few  drops 
of  ammonium  acetate  are  then  added,  and  the  filtrate  is  evapo- 
rated so  far  that  the  solution  will  be  contained  in  the  beaker- 
.glass,  in  which  it  is  intended  to  make  the  electrolytic 
precipitation.  The  fluid  is  then  filtered  into  this  beaker  from 
the  small  quantity  of  iron  sediment,  supersaturated  with  ammo- 
nia, etc. 

Instead  of  supersaturating  the  solution  with  ammonia,  it  is  bet- 
ter to  add  20  cubic  centimeters  of  ammonia,  and  the  same  quan- 
tity of  ammonium  sulphate,  and  to  electrolyze  it  in  the  apparatus 
used  for  the  galvanic  assay  of  copper  (p.  110).  The  binding 


196  ASSAYING. 

screws  of  the  electrode  should  be  well  coated  with  shellac  to  pro- 
tect them  against  corrosion  by  the  ammoniacal  vapors. 

In  the  presence  of  much  iron,  and  of  ammonium  chloride, 
chlorine,  which  attacks  the  platinum,  will  be  developed  on  the 
positive  electrode.  For  this  reason  a  sulphuric  acid  solution  is  to 
be  preferred,  and  ammonium  sulphate  exerts  a  favorable  effect 
upon  the  process. 

As  the  ammoniacal  nickel  solutions  oifer  greater  resistance  to 
the  galvanic  current  than  the  acid  copper  solutions,  the  nickel 
will  be  principally  deposited  on  the  inner  sides  and  lower  end  of 
the  platinum  cone,  where  small  bubbles  of  hydrogen  may  also 
make  their  appearance,  causing  the  nickel  to  be  deposited  in  fine, 
non-coherent  laminae,  which  spring  oif  in  the  subsequent  rinsing 
and  drying,  thus  occasioning  losses.  This  mast  be  avoided  by 
suspending  the  platinum  cone  in  such  a  manner  that  its  lower 
edges  shall  be  about  1.5  centimeters  above  the  bottom  of  the 
glass ;  further,  by  increasing  the  electrical  conductivity  of  the  so- 
lution by  an  addition  of  ammonium  sulphate,  and  by  using  a  cur- 
rent sufficiently  strong  to  give  at  least  100  cubic  centimeters  of 
oxyhydrogen  gas  in  the  voltameter  in  half  an  hour.  A  black 
coating  of  nickel  sesquioxide,  which  may  be  formed  on  the  posi- 
tive electrode,  will  generally  disappear  by  strongly  supersatura- 
ting the  fluid  with  ammonia.  Should  this  not  produce  the  desired 
effect,  the  platinum  cone  is  first  taken  out,  placed  in  water,  the 
spiral  is  then  removed,  and  a  few  drops  of  hydrochloric  acid  are 
allowed  to  drip  down  on  it,  which  will  cause  the  coating  to  dis- 
solve with  evolution  of  chlorine.  Some  ammonia  is  then  added, 
and  the  apparatus  again  put  in  place  and  allowed  to  operate  for  a 
few  hours  longer.  Should  ferric  hydrate  be  separated,  it  is  col- 
lected, in  case  it  is  to  be  determined  by  volumetric  assay,  and , 
added  to  that  first  obtained.  After  an  electrolyzation  of  about 
18  hours,  the  platinum  cone  is  taken  out,  placed  in  a  beaker-glass 
containing  water,  and  rinsed  oif  with  hot  water.  It  is  then  taken 
out  and  placed  upon  several  thicknesses  of  filter  paper.  From 
here  it  is  brought  into  a  beaker-glass  containing  alcohol,  alcohol 
being  likewise  allowed  to  run  down  on  the  wire.  The  cone  is 
next  placed  upon  blotting  paper  and  then  completely  dried  upon 
a  sheet-iron  plate  heated  over  a  lamp.  After  it  has  become  cool, 


NICKEL — WET   ASSAY.  197 

it  is  weighed  and  the  nickel  (or  nickel  and  cobalt)  is  ascertained 
from  the  increase  in  weight. 

When  zinc  is  present,  some  of  which  is  precipitated  along  with 
nickel  (hydrochloric  and  nitric  acid,  and  their  salts,  prevent  this 
precipitation,  but  sulphuric  acid  does  not),  the  hydrochloric  Dr 
nitric  acid  solution  is  treated,  after  driving  off  the  sulphuretted 
hydrogen,  with  sodium  carbonate  until  it  exhibits  only  a  slight 
acid  reaction.  More  sulphuretted  hydrogen  is  then  introduced, 
in  order  to  precipitate  zinc  sulphide,  until  no  further  increase  of 
the  precipitate  is  perceptible;  a  drop  of  a  diluted  solution  of 
sodium  acetate  is  then  added.  Sulphuretted  hydrogen  is  now 
again  introduced  for  some  time,  and  the  liquid  then  allowed  to 
stand  quietly  for  twelve  hours.  It  is  then  filtered  and  washed 
with  sulphuretted  hydrogen  water.  The  zinc  sulphide  is  dis- 
solved in  hydrochloric  acid,  and  precipitated,  after  the  sul- 
phuretted hydrogen  has  been  expelled,  by  sodium  carbonate ;  or 
the  zinc  sulphide,  with  the  addition  of  some  sulphur,  is  ignited  in 
a  current  of  hydrogen  gas  (p.  117).  The  nickeliferous  filtrate, 
from  the  precipitate  with  sulphuretted  hydrogen,  is  heated,  some 
ammonia  added,  and  it  is  then  electrolyzed,  after  the  iron  has 
been  separated  in  the  manner  indicated  on  p.  195. 

The  platinum  cone  coated  with  cobalt  and  nickel  is  placed  in  a 
beaker-glass,  and  covered  with  a  mixture  of  1  part  of  nitric 
acid,  of  1.2  specific  gravity,  and  3  parts  of  water.  This  is  heated 
until  solution  of  the  metallic  deposit  is  complete.  The  cone  is 
then  taken  out  and  rinsed  off  with  hot  water.  The  solution  is 
evaporated  to  a  small  volume,  and  some  potassium  hydrate  added 
until  precipitation  just  begins.  The  precipitate  is  dissolved  by 
the  addition  of  some  acetic  acid,  a  concentrated  solution  of 
potassium  nitrate  is  added,  and  the  fluid  allowed  to  stand  for  24 
hours.  The  yellow  precipitate  of  CO(NO2)3  +  3KNO2  is  filtered 
off',  and  washed  first  with  potassium  acetate  and  then  with  alcohol. 
It  is  next  dissolved  in  sulphuric  acid,  and  digested  until  the  odor 
of  nitrous  acid  has  been  entirely  dispelled.  It  is  then  neutralized 
with  ammonia,  20  cubic  centimeters  of  ammonium  sulphate  and 
the  same  quantity  of  ammonia  are  added,  and  the  solution  again 
subjected  to  electrolyzation.  The  cobalt  is  weighed,  and  the 
nicllel  determined  from  the  difference. 


198  ASSAYING. 

Determination  of  nickel  in  pyrites  and  matt.1 — 2  to  5  grammes 
of  the  substance  are  dissolved  in  hydrochloric  acid,  to  which  some 
nitric  acid  has  been  added,  and  the  solution  precipitated  with  sul- 
phuretted hydrogen  (p.  194).  The  filtrate  is  boiled  in  order  to 
expel  the  sulphuretted  hydrogen,  and  nitric  acid  or  potassium 
chlorate  is  added  to  oxidize  ferrous  to  ferric  oxide.  Ammonia 
is  then  added  until  some  precipitate  forms,  but  without 
precipitation  being  complete.  Some  acetic  acid  is  now  added 
until  a  deep-red  solution  is  formed.  This  is  boiled,  and  a  solu- 
tion of  concentrated  sodium  phosphate  is  added  in  excess.  The 
precipitate  of  iron  is  filtered  off  and  washed  with  hot  water  con- 
taining some  acetic  acid.  The  filtrate  is  boiled,  and  potassium 
hydrate  added  until  an  odor  of  ammonia  is  clearly  perceptible. 
The  apple-green  nickel  phosphate  is  washed  out,  dissolved  in 
diluted  sulphuric  acid,  and  made  strongly  alkaline  by  addition  of 
ammonia.  The  solution  is  then  subjected  to  electrolyzation. 
When  more  than  3  per  cent,  of  nickel  is  present,  the  precipitate 
of  iron  is  again  dissolved,  reprecipitated,  etc.  A  trace  of  iron, 
but  not  enough  to  influence  the  precipitation  of  nickel  by  the 
battery,  may  remain  in  the  solution  if  too  small  a  quantity  of 
sodium  phosphate  is  present,  or  if  the  solution  was  made  alkaline 
before  the  addition  of  acetic  acid. 

Assay  of  New  Caledonia  ores. — Allen2  recommends  the  follow- 
ing process  for  the  examination  of  these  ores  (which  are  a  silicate 
of  magnesium  containing  nickel),  or,  in  general,  for  ores  containing 
neither  sulphur  nor  arsenic:  Fuse  2  grammes  of  ore  in  a  platinum 
crucible  with  potassium  bisulphate  and  nitre,  lixiviate  with  water, 
boil  the  residue  with  some  HC1  and  filter  the  whole.  Neutralize 
carefully  with  ammonia,  add  excess  of  ammonium  acetate  and  boil, 
thus  precipitating  the  iron,  alumina,  and  chromic  oxide.  Dissolve 
the  precipitate  in  HC1  and  again  precipitate  in  same  manner.  Boil 
the  combined  filtrates,  add  sufficient  ammonia  to  nearly  neutralize 
the  acetic  acid,  then  pass  H2S  through  the  solution  whilst  hot. 
Wash  the  precipitate  of  nickel  sulphide  (perhaps  also  some  cobalt 
sulphide)  with  water  containing  H2S  and  ammonium  acetate,  then 
dissolve  this  precipitate  in  HN03  and  add  some  H2S04.  Add 

1  B.  u.  h.  Ztg.  1878,  p.  41. 

2  Bullet,  de  la  Socie~te  d' Encouragement,  t.  vi.  p.  36  (1879). 


NICKEL — WET   ASSAY.  199 

excess  of  ammonia,  filter  off  the  slight  precipitate  which  may  form 
and  subject  the  ammoniacal  solution,  in  a  platinum  dish,  to  electro- 
lysis, care  being  observed  that  the  solution  constantly  shows  an 
ammoniacal  reaction.  In  all  the  electrolytic  precipitations  of  nickel 
(cobalt)  the  solution  must  always  contain  an  excess  of  free  ammonia. 
The  presence  of  ammonium  sulphate  promotes  the  separation  of  the 
metals,  but  that  of  ammonium  chloride  or  nitrate  hinders  or  pre- 
vents it.  Too  much  ammonia,  however,  is  not  good,  as  it  opposes 
considerable  resistance  to  the  electric  current.  Braun  recommends 
the  use  of  potassium  sulpho-carbonate  for  indicating  the  end  of  the 
precipitation ;  its  reaction  with  nickel  is  very  sensitive.  The  pre- 
cipitation may  be  regarded  as  finished  when  a  sample  of  the  nickel 
solution  acquires  only  a  very  slight  rose  color.  Classen's  method 
for  the  determination  of  nickel  by  electrolysis  is  exactly  the  same  as 
for  zinc. 

Electrolytic  determination  of  copper,  nickel,  and  cobalt  in  speiss. 
— According  to  Ohl,1  the  process  is  as  follows :  Digest  one  gramme 
of  the  finely  pulverized  speiss  in  a  covered  beaker  (of  200  c.c.  capa- 
city) with  HN03  or  HN03  +  HC1  and  evaporate  to  dryness.  Add 
enough  concentrated  HC1  to  cover  the  dry  residue  to  a  height  of 
5  millimeters,  and  after  solution  has  taken  place  dilute  with  water 
up  to  half  the  height  of  beaker.  Heat  and  pass  HaS  through  solu- 
tion until  it  is  cold,  then  reheat  and  repeat  this  operation.  If  only 
arsenious  sulphide  has  been  precipitated,  again  the  warm  solution 
until  the  odor  of  H2S  can  no  longer  be  detected.  If  the  precipitate  is 
not  pure  yellow,  but  is  discolored  (probably  cupreous),  filter  until  the 
solution  has  no  further  odor  of  H2S  and  wash  with  water  containing 
H2S,  using,  however,  only  pure  cold  water  if  arsenic  alone  is  pre- 
cipitated. After  adding  potassium  chlorate  to  oxidize  any  iron 
present,  evaporate  the  filtrate  containing  nickel  and  cobalt  to  dry- 
ness,  take  up  with  water  and  HC1  and  mix  with  pure  soda  solution 
until  alkaline  reaction.  The  precipitate  is  then  dissolved  in  acetic 
acid,  and  the  solution  largely  diluted  and  boiled.  Filter  and  wash  with 
hot  water  until  a  drop  of  wash  water  produces  no  turbidity  with 
ammonium  sulphide.  If  zinc  is  present,  acetic  acid  must  no  w  be  added 
and  the  zinc  precipitated  with  H2S.  The  zinc  sulphide  filtered  off, 
filtrate  evaporated  to  dryness,  taken  up  with  water  and  H2S04,  satu- 
rated with  ammonia  and  the  solution  subjected  to  the  electric  current. 
When  the  solution  of  nickel  and  cobalt  becomes  discolored  it  is 

i  Ztschft.  f.  Anal.  Chein.  Bd.  18,  p.  523. 


200  ASSAYING. 

tested  with  ammonium  sulphide  to  see  if  the  precipitation  is  com- 
plete. It  is  better  after  dissolving  the  metals  from  the  electrode  to 
separate  the  cobalt  by  potassium  nitrite  and  after  dissolving  the 
yellow  salt  formed  and  saturating  with  ammonia  to  determine  the 
cobalt  by  electrolysis.  In  the  simultaneous  presence  of  both  arsenic 
and  copper  they  are  separated  in  the  following  manner  :l  Pass  H2S 
slowly  through  the  original  solution  (previously  filtered  and  cooled 
if  necessary),  whereby  the  copper  sulphide  separates  out  in  flakes 
and  the  supernatant  liquid  is  clear  when  held  to  the  light.  It  is 
claimed  that  in  this  manner  the  copper  can  be  sharply  separated 
from  the  arsenic.  After  filtering  and  washing,  the  precipitate  is 
dissolved  in  HN03,  evaporated  to  dryncss,  taken  up  with  20  c.c.  of 
HN03,  and  after  diluting  to  200  c.c.  with  water  the  solution  sub- 
jected to  action  of  electric  current.  The  filter  paper  may  be  al- 
lowed to  remain  in  the  solution  so  treated  without  doing  harm. 
In  the  presence  of  only  a  small  amount  of  arsenic  the  copper  is  first 
precipitated.  The  solution  thus  freed  from  copper  is  added  to  the 
filtrate  from  the  copper  sulphide,  the  arsenic  completely  precipitated 
with  H2S,  the  arsenious  sulphide  filtered  off,  dissolved  in  aqua  regia, 
saturated  with  ammonia  and  precipitated  as  ammonium-magnesium 
arsenate.  If  in  the  electrolytic  precipitation  of  the  nickel  and  cobalt 
some  iron  appears  it  is  filtered  off,  added  to  that  already  precipitated 
out,  the  whole  dissolved  in  HC1,  and  the  iron  determined  by  titra- 
tion  with  proto-chloride  of  tin.  If  antimony  is  also  present,  it  is 
separated  as  antimonic  oxide  by  twice  evaporating  the  precipitated 
metallic  sulphide  with  HN03, 

2.   Other  assays.2 

a.  The  ore,  etc.,  is  dissolved  in  aqua  regia  and  evaporated  with 
the  addition  of  sulphuric  acid.  Aqueous  sulphurous  acid  is  added 
to  this  in  order  to  reduce  the  arsenic  acid.  The  sulphurous  acid 
is  then  removed  by  boiling,  and  the  copper,  arsenic,  etc.,  are  pre- 
cipitated with  sulphuretted  hydrogen.  The  liquid  is  then  filtered, 
the  sulphuretted  hydrogen  removed  by  evaporation,  and  the  fer- 
rous oxide  oxidized  by  potassium  chlorate.  Sodium  carbonate, 
boiling  hot,  is  then  added  until  a  permanent  precipitate  is  formed. 
A  drop  of  hydrochloric  acid  is  now  added,  until  the  precipitate 

1  Fortschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  151. 

2  Fresenius's  Verfahren  fiir  Erze,  Leche  und  Speisen  in  Fresenius's  Ztschr. 
xii.  70. 


NICKEL — WET   ASSAY.  201 

just  disappears,  and  then  a  large  quantity  of  sodium  acetate  added 
to  the  hot  solution.  This  is  boiled  for  10  to  15  minutes,  and  the 
precipitate  of  iron  and  alumina  quickly  filtered  off,  washed,  and 
again  dissolved  in  hydrochloric  acid,  etc.,  in  order  to  separate 
such  traces  of  nickel  as  it  may  contain.  Chlorine  water  is  added 
to  the  nickeliferous  filtrate,  followed  by  potassium  hydrate  (some 
/inc  also  will  be  precipitated),  and,  if  necessary,  more  chlorine 
water.  This  is  boiled  for  a  quarter  of  an  hour,  or  until  the  pre- 
cipitate of  nickel  and  cobalt  sesquioxides  has  assumed  a  black 
color.  It  is  then  filtered,  the  precipitate  dried,  and  the  oxides 
reduced  in  a  current  of  hydrogen  gas  (p.  117).  For  the  separation 
of  nickel  and  cobalt,  the  weighed  metals  are  dissolved  in  hydro- 
chloric acid.  The  solution  is  slightly  supersaturated  with  sodium 
carbonate.  A  concentrated  solution  of  potassium  nitrite  is  added, 
an  i  then  some  acetic  acid  until  a  weak  acid  reaction  is  estab- 
lished. The  liquid  is  then  allowed  to  stand  for  24  hours,  when 
the  yellow  cobalt  precipitate  is  filtered  off  and  washed  with  a  con- 
centrated solution  of  potassium  chloride,  or  potassium  sulphate. 
The  precipitate  is  now  dissolved  in  hydrochloric  acid,  the  solution 
precipitated  with  sodium  hydrate  and  chlorine  water,  etc.,  and 
the  cobalt  sesquioxide  reduced  in  a  current  of  hydrogen  gas.  The 
solution  carrying  the  nickel  is  precipitated  with  potassium  hy- 
drate and  chlorine  water,  etc. 

In  order  to  separate  the  iron,  the  oxidized  iron  is  partly  precip- 
itated with  sodium  carbonate  (p.  200).  Some  acetic  acid  is 
added,  and  the  liquid  is  heated  to  30°  to  40°  C.  (86°  to  104°  F.) 
in  order  to  dissolve  the  precipitated  iron.  It  is  then  boiled,  the 
precipitated  iron  is  again  dissolved  two  or  three  times,  and  the 
precipitation  repeated  to  separate  the  nickel  from  it.  Finally,  by 
adding  sodium  sulphide  the  ferric  oxide  is  converted  into  iron 
sulphide,  and  this  is  treated  with  diluted  hydrochloric  acid, 
whereby  a  trace  of  nickel  sulphide  may  still  be  found  in  the  resi- 
due. 

b.  Nickeliferous  solution  from  the  assay  with  sulpho-cyanide  for 
determining  copper  in  nickel  coins. — In  order  to  decompose  the 
sulpho-cyanide,  the  solution  is  evaporated  with  the  addition  of 
10  cubic  centimeters  of  nitric  acid,  which  will  cause  the  fluid  to 
become  first  red,  and  then  colorless.  The  nickel  is  precipitated 


202  ASSAYING. 

by  pouring  the  nickeliferous  liquid  into  a  boiling  solution  of  100 
cubic  centimetres  of  sodium  hydrate,  10  per  cent,  strength,  which 
is  boiling  in  a  platinum  evaporating  dish.  It  is  allowed  to  boil, 
then  diluted  with  water,  and  again  heated  to  the  boiling  point. 
It  is  allowed  to  settle,  and  then  decant  through  a  filter.  The 
precipitate  is  again  boiled  three  times,  each  time  with  200  cubic 
centimeters  of  water,  and  then  filtered.  The  precipitate  is  dried, 
heated  to  redness,  and  rubbed  fine,  again  washed  with  boiling 
water,  dried,  ignited,  and  the  nickel  determined  from  the  nickel 
protoxide1  (now  free  from  alkali)  with  78.38  per  cent,  nickel. 

Inaccurate  results  will  follow  if  less,  or  less  concentrated, 
sodium  hydrate  is  used,  or  if  the  washing  is  continued  too  long, 
as  under  these  circumstances  some  nickel  is  dissolved  as  hydrated 
oxide. 

E.  Volumetric  assay  with  sodium  sulphide? — The  copper  which 
may  be  present  is  removed  by  means  of  sulphuretted  hydro- 
gen, and  its  percentage  determined  by  the  potassium  cyanide 
(p.  120).  The  filtrate  from  the  precipitation  with  sulphuretted 
hydrogen  is  evaporated  with  nitric  acid,  and  the  iron  precipitated 
with  ammonia.  The  precipitate  is  dissolved  twice  or  three  times, 
and  again  precipitated  with  ammonia  (the  methods  with  ammo- 
nium sesquicarbonate  or  with  sodium  acetate  (p.  201)  give  a 
more  accurate  separation) ;  a  standard  solution  of  sodium  sul- 
phide, 50  cubic  centimeters  of  which  precipitate  0.25  gramme  of 
nickel,  is  then  added  to  the  vigorously  boiling  solution,  until  all 
the  nickel  (with  cobalt)  has  been  separated.  The  addition  of 
sodium  sulphide  is  made  in  quantities  of  not  more  than  J  cubic 
centimeter  at  a  time,  the  solution  being  maintained  at  the  boiling 
point,  until  a  filtered  drop  becomes  brown  when  brought  in  con- 
tact with  lead  solution  upon  a  porcelain  plate. — The  solution  of 
lead  is  prepared  by  dissolving  equal  quantities  of  lead  acetate  and 
potassium  tartrate  in  caustic  potassa.  The  normal  solution  is 
prepared  by  dissolving  0.25  gramme  of  pure  nickel  (or  cobalt), 
or  an  equivalent  quantity  of  pure  oxide  or  salt,  in  5  cubic  centi- 
meters of  concentrated  nitric  acid.  This  is  diluted  with  water, 

1  Fresenius's  Ztschr.,  1878,  p.  58. 

2  Journal  fur  prakt.  Chemie,  Ixxxviii.  486  (Kuntzel)  ;  xcii.  450  (Winkler) ; 
Fresenius's  Ztschr.  vi.  66  (Braun). 


NICKEL  —  WET  ASSAY.  203 

supersaturated  with  ammonia,  tested  with  a  saturated  solution  of 
sodium  sulphide,  which  is  thereupon  suitably  diluted. 

Separation  of  cobalt.  —  The  metallic  sulphides  of  nickel  and 
cobalt,  which  have  been  precipitated  with  sodium  sulphide,  are 
filtered  off,  and  the  precipitate  is  washed  with  sulphuretted  hydro- 
gen water.  It  is  then  dissolved  in  aqua  regia  and  evaporated 
with  hydrochloric  acid  to  expel  the  nitric  acid.  It  is  now  strongly 
diluted  with  water  in  a  suitable  flask,  and  nearly  neutralized. 
Elutriated  barium  carbonate  is  added,  chlorine  gas  introduced, 
and  the  precipitated  black  cobalt  sesquioxide  dissolved  in  hydro- 
chloric acid.  The  barium  is  precipitated  with  sulphuric  acid,  am- 
monia in  excess  is  added,  and  the  cobalt  titrated  with  solution  of 
sodium  sulphide.  The  barium  is  then  precipitated  from  the  nickel- 
iferous  filtrate,  ammonia  is  added,  and  the  nickel  similarly  titrated 
with  solution  of  sodium  sulphide.  When  zinc  and  manganese  are 
present,  the  ores  are  fused  with  potassium  cyanide,  arsenious  acid, 
soda,  and  black  flux,  to  a  button  containing  all  the  nickel  and 
cobalt,  as  well  as  a  part  of  the  copper  and  iron,  while  zinc  and 
manganese  are  slagged  off.  The  button  is  dissolved  in  aqua 
regia,  the  copper  and  arsenic  are  precipitated,  hot,  with  sulphur- 
etted hydrogen,  and  the  nickel  and  cobalt  determined  as  above. 

Volumetric  assay  of  nickel  and  cobalt  according  to  Donath.1  — 
This  determination  is  based  upon  the  following  behavior  of  the  two 
metallic  oxides.  In  mixing  a  solution  of  nickel  and  cobalt  with  an 
excess  of  caustic  soda  or  potash  and  iodine,  and  boiling,  the  cobalt 
is  completely  converted  into  oxide,  while  the  nickel  protoxide 
remains  unchanged.  This  nickel,  however,  can  be  more  highly  ox- 
idized with  bromine.  The  process  is  as  follows  :  divide  the  solution 
of  the  two  metals  into  equal  parts,  mix  one  part  with  caustic  pot- 
ash and  bromine,  and  boil,  whereby  both  metals  are  precipitated  as 
sesquioxides.  The  other  part  is  treated  with  caustic  potash  and 
iodine,  the  cobaltous  oxide  alone  is  precipitated.  The  two  precipi- 
tates are  thoroughly  washed,  transferred  into  separate  flasks,  and 
boiled  with  HC1.  The  chlorine  developed  is  taken  up  by  a  solution 
of  potassium  iodide,  the  well-known  apparatus  used  by  Mohr  for 
the  volumetric  determination  of  manganese  (Fig.  80)  being  used 
for  the  purpose.  The  reaction  is  expressed  as  follows  :  — 
R203+6HCl=2RCl2-{-3H2 


Oesterr.  Ztschft.  f.  Bg.  u.  Httnwsn,  1879,  p.  550. 


204  ASSAYING. 

Hence,  1  atom  of  iodine  corresponds  to  1  atom  of  cobalt  or  nickel. 
The  iodine  liberated  by  boiling  both  precipitates  is  determined  with 
T^  normal  solution  of  sodium  hyposulphite.  The  difference  between 
the  two  determinations  corresponds  to  the  content  of  nickel,  its 
weight  being  computed  by  multiplying  by  0.0059.  With  one  portion, 
however,  only  the  precipitated  cobalt  is  determined,  and  the  number 
of  c.c.  of  the  hyposulphite  used  is  multiplied  by  0.0059  (since  the 
atomic  weight  of  both  metals  is  the  same). 

C.  Colorimetric  assay} — A  eolorimetric  method  for  determining 
nickel  has  been  proposed  by  Winkler,  but  it  is  of  little  practical 
value. 

VII,  COBALT, 

42.    ORES. 

Smaltine,  CoAs2,  with  28.19  Co;  cobalt  glace  (cobaltine),  CoAsS, 
with  35.5  Co ;  cobalt  pyrites  (linnaeite)  (NiS.CoS.FeS)  (Ni2S3.Cor 
S3.Fe2S3),  with  14.6  Ni  and  11  to  40.7  Co  ;  glaucodot  (FeCo)  AsS, 
with  24.77  Co;  earthy  cobalt,  (CoO.CuO)  2MnO2  +  4H2O  ;  cobalt 
bloom,  Co3As2O8+8H2O,  with  37.5  CoO  =  29.5  Co. 

43.   ASSAYS  OF  COBALT. 

The  object  of  the  assays  is — 

1.  The  determination  of  cobalt  by  the  dry  (p.  188)  or  the  wet 
method  ;  in  the  latter  case  by  gravimetric  (p.  200)  and  volumetric 
analysis  (p.  202),  of  which  the  details  have  already  been  given 
in  the  foregoing  chapter  on  Nickel. 

2.  The  determination  of  the  blue  coloring  powder  (density),  and 
the  beauty  of  the  colors  (smalt  colors)  which  are  formed  in  fusing 
ores  and  products  containing  cobaltous  oxide  with  different  quan- 
tities of  potassium  silicates  (smalt  assay). 

44.    SMALT   ASSAY. 

Cobaltous  oxide,  either  contained  as  such  in  the  ores  (earthy 
cobalt,  cobalt  bloom),  or  produced  by  roasting  sulphurized  and 

1  Journ.  f.  prakt.  Chem.,  xcvii.  414. 


COBALT — SMALT   ASSAY.  205 

arsniized  ores,  gives  a  blue  color  to  fused  potassium  silieate 
(smalt  glass,  very  likely  CoO.3SiO2  -f  K2O.3SiO2),  the  color, 
under  otherwise  equal  conditions,  being  the  more  intense,  the 
rid  HT  the  ore  in  cobaltous  oxide.  The  presence  of  foreign  metallic 
oxides,  which  alse  dissolve  in  potassium  silicate,  exerts  an  in- 
jurious effect  upon  the  beauty  of  the  blue  tint. 

Nickel  protoxide,  the  most  injurious  foreign  substance,  produces 
an  objectionable  reddish  or  violet  tint;  ferrous  oxide,  if  present  in 
small  quantities,  gives  a  greenish  shade,  but  ferric  oxide,  bismuth 
o.ridc,  lead  oxide,  and  manganous  oxide  affect  the  cobalt  color  to  a 
very  small  extent  only.  Manganic  oxide  gives  a  violet  tint ; 
cuj)ric  oxide,  a  green ;  cuprous  oxide,  a  red  tint ;  while  the  color- 
ing power  of  manganous  oxide  is  counteracted  by  that  of  ferrous 
oxide,  if  both  are  present. 

In  roasting  arsenized  and  sulphurized  cobalt  ores,  the  various 
metals  become  oxidized  in  succession,  cobalt  the  soonest  of  them 
all,  so  that  it  becomes  necessary  to  conduct  the  roasting  of  the 
ores  in  such  a  manner  that  cobaltous  oxide  only  is  produced, 
which,  on  being  fused  with  silicic  acid  and  potash,  gives  the  beau- 
tifully colored  smalt.  The  foreign  metals  should  not  become 
oxidized,  but  remain  combined  with  arsenic  or  sulphur,  forming 
a  cobalt  speiss. 

As,  in  roasting  the  above-named  arsenides  and  sulphides,  cobalt 
is  first  oxidized,  and  iron  and  bismuth  earlier  than  copper  and 
nickel,  wes  containing  copper  and  nickel  must  not  be  roasted  too 
strongly,  and  least  of  all  dead-roasted  ;  this  may,  however,  be 
done  with  entirely  pure  ores  of  cobalt,  or  such  as  contain  only  iron, 
as,  in  the  latter  case,  ferric  oxide  is  formed,  which  only  slightly 
affects  the  cobalt  color.  If  impure  ores  are  roasted  too  little,  a 
beautiful  smalt  is  formed,  but  much  cobalt  is  lost  in  the  speiss. 

The  object  of  the  smalt  assay  is  either,  a,  the  determination  of 
the  coloring  power  of  a  sample  (assay  for  determining  the  intensity 
of  the  color),  or,  b,  to  ascertain  the  degree  of  roasting  to  which  the 
ore  must  be  subjected  in  order  to  obtain  a  color  of  pure  quality 
(assay  to  determine  the  color  tone),  or,  c,  to  determine  how  much 
of  an  already  known  sample  must  be  taken  to  produce  a  certain 
shade  of  color. 

Several  lots  of  ore,  each  from  1  to  5  grammes  according  to  the 


206  ASSAYING. 

richness  of  the  ore,  are  weighed  off.  The  separate  lots  are  each 
roasted  for  a  different  length  of  time  (for  instance,  the  first  lot 
J  of  an  hour,  and  the  subsequent  lots  each  from  10  to  15  minutes 
longer),  while  one  of  the  samples  is  left  unroasted.  Each  sample 
is  divided  by  weighing  into  two  equal  parts,  of  which  one  is  tested 
with  fluxes  to  determine  the  quality  of  color,  and  the  other  its 
intensity. 

A.  Assay  to  determine  the  quality  of  color. — Each  sample  is 
mixed  with  three  times  the  quantity,  by  weight,  of  quartz  free 
from  iron  and  manganese,  and  with  a  quantity  of  pure  potash 
corresponding  to  half  the  combined  weight  of  quartz  and  ore. 
The  mixture  is  placed  in  flat  dishes  of  white  fire-clay  (smalt- 
dishes).     It  is  then  fused  in  the  muffle  (Fig.  27,  p.  47),  which 
should  be  heated  as  strongly  as  possible,  until  a  completely  homo- 
geneous glass   has  been  formed   (this  will  require  4  hours  or 
longer).     A  sample  is  then  taken  from  the  charge  by  means  of  a 
pair  of  tongs  and  cooled  off  in  water.     The  mass  is  dried  and 
pounded  in  a  bright  steel  mortar,  in  order  to  obtain  angular  frag- 
ments (powdered  smalt  is  apt  to  appear  dirty).     The  fragments 
are  sifted  upon  white  paper,  and,  without  taking  intensity  into 
consideration,  a  judgment  is  formed  at  which  degree  of  roasting 
the  most  beautiful  color  has  been  obtained. 

B.  Assay  to  determine  the  intensity. — The  assay  sample  is  fused 
in  the  above  manner  with  different  quantities  of  quartz  (for  in- 
stance, 1  to  10  times  the  quantity),  and  half  the  quantity  of 
potash,  to  a  homogeneous  cobalt  glass.     Generally  2.5  grammes 
of  the  assay  sample  are  taken  when  it  has  been  mixed  with  once 
or  twice  the  quantity  of  quartz,  and  1.25  grammes  if  with  more 
quartz,  to  prevent  the  crucibles  from  becoming  too  full.     Too 
much  quartz  makes  it,  difficult  to  fuse  the  mixture,  and  too  much 
potash  gives  smeary  colors.     A  sample  is  taken  from  the  smelted 
mass,  cooled  off  and  dried.     It  is  then  pounded  and  sifted,  or 
washed  in  spitz-glasses  (Fig.  4,  p.  26),  and  its  color  compared 
with  that  of  a  standard,  as  to  color  and  grain.     This  is  done 
by  spreading  some  of  the  standard  color  with  a  knife  evenly 
upon  a  board,  and  placing  a  quantity,  as  large  as  a  pea,  of  the 
assay  sample  upon    it  and  pressing  the  latter  into  the  former, 
when  an  experienced  eye  can  tell  in  a  well  lighted  room  (not 


ZINC — DRY   ASSAYS.  207 

exposed  to  the  direct  rays  of  the  sun)  whether  the  assay  sample 
corresponds  with  the  standard  in  color-tone  and  grain,  or  not.  If 
it  should  correspond  in  all  respects,  a  confirmatory  test  is  made 
by  pressing  some  of  the  standard  into  the  assay  sample,  when  the 
same  conditions  must  exist,  and  by  examining  the  grain  in  both 
cases  with  a  magnifying  glass. 

As  moist  smalt  appears  darker  than  dry,  the  standard  and 
assay  sample  must  stand  for  from  6  to  8  hours  alongside  of  each 
other  in  a  somewhat  damp  place,  before  the  examination  is  made. 
The  intensity  of  the  color  also  increases  with  the  coarseness  of  the 
grain,  and  an  experienced  eye  and  skilful  hand  are  required  to 
give  the  assay  sample  taken  from  the  fused  mass,  the  same  grain 
as  the  standard  with  which  it  is  to  be  compared.  If  the  color  of 
the  assay  sample  is  lighter  than  the  standard  with  which  it  is 
compared,  the  assay  must  be  repeated,  with  a  larger  quantity  of 
ore,  and  vice  versa.  If  the  color  is  not  exactly  the  same,  recourse 
is  frequently  had  to  mixing  the  product  with  lighter  or  darker 
varieties  of  smalt.  An  ore  is  the  more  valuable,  the  more  quartz 
it  requires  for  the  production  of  a  certain  intensity  of  color. 

VIII,  ZINC, 

45.    ORES. 

Smithsonite  (zinc  carbonate),  ZnCO3,  with  52Zn  ;  calamine  (zinc 
silicate),  Zn2SiO4  +  3H2O,  with  53.7  Zn ;  willemite,  Zn^SiO,,  with 
58.1  Zn;  zinc  bloom,  Zn3CO5+2H2O,  with  57.1  Zn ;  zinc  blende, 
ZnS,  with  67.01  Zn ;  zinkite,  ZnO,  with  80.24  Zn ;  franklinite, 
(Zn,  Fe)  (Fe2Mn2)O4,  with  21  Zn. 

46.    DRY   ASSAYS. 

These  are  inaccurate,  but  give  approximately  the  quality  of  the 
metal  which  may  be  expected  from  an  ore  (distillation  assay),  or 
the  approximate  percentage  of  zinc.  For  many  purposes  they 
are  sufficiently  accurate  (indirect  assay). 

A.  Assay  by  distillation. — A  mixture  of  400  to  500  grammes 
of  the  comminuted  assay  sample  with  80  to  100  per  cent,  of 


208  ASSAYING. 

powdered  charcoal,  and,  in  case  calamine  is  to  be  assayed,  with 
80  to  100  grammes  of  potash  or  calcined  soda,  is  placed  in  a 
retort  of  refractory  clay  and  heated  in  a  furnace  with  a  strong 
draught  (Fig.  32,  p.  51).  The  neck  of  the  retort  should  project 
about  10  centimeters.  In  it  is  luted  a  tube  of  glass  or  porcelain 
about  30  centimeters  long,  wrhich  is  kept  cool  by  moistened  rags 
wrrapped  around  it.  The  burning  gases  and  the  fumes  escape 
from  the  end  of  the  tube,  while  the  zinc,  mixed  with  oxide,  wrhich 
is  distilled  over,  is  mostly  deposited  in  the  neck  of  the  retort  and 
but  little  of  it  in  the  tube.  After  the  "  flaming"  ceases,  the  tube 
should  be  frequently  poked  with  an  iron  wire.  The  retort,  after 
having  been  exposed  to  a  white  heat  for  several  hours  and  the 
"  flaming"  having  entirely  ceased,  is  taken  from  the  furnace  and 
allowed  to  cool  oiF.  The  metallic  zinc  is  scraped  from  the  neck 
of  the  retort,  is  placed  in  a  crucible  and  fused  with  black  flux 
and  a  covering  of  common  salt.  It  is  then  poured  out  into  an 
ingot  mould  and  weighed.  The  retort  is  carefully  broken  into 
pieces,  and  all  those  having  adhering  to  them  either  zinc  or  zinc 
oxide  are  collected  together  and  placed  in  a  porcelain  dish,  and 
the  metal  dissolved  off  by  digestion  with  nitric  acid.  The  solu- 
tion is  filtered  and  evaporated  to  dry  ness.  The  residue  is  heated 
to  redness,  the  zinc  calculated  from  the  resulting  zinc  oxide,  with 
80.24  per  cent,  of  zinc  and  added  to  the  metallic  zinc. 

B.  Indirect  assay. — 5  grammes  of  zinc  blende  are  placed  in  a 
covered  crucible  (Fig.  49,  p.  64)  and  heated  under  the  muffle  in 
order  to  expel  the  volatile  substances.  After  it  has  been  cooled 
off,  it  is  weighed  and  the  ignition  repeated  until  a  constant  weight 
is  obtained.  The  accurately  weighed  refractory  residue  is  mixed 
with  3  grammes  of  iron  filings  free  from  rust,  and  2.5  grammes 
of  blast-furnace  slag.  The  mixture  is  brought  into  a  charcoal- 
lined  iron  crucible  (Fig.  53,  p.  65),  covered  with  2.5  grammes 
of  blast-furnace  slag,  and  the  remaining  space  filled  up  with 
powdered  charcoal.  A  loosely  fitting  cover  is  luted  on.  The 
charge  is  then  heated  at  a  white  heat  in  the  blast-furnace  for  }  to 
1  hour,  whereby  iron  sulphide  is  formed,  while  zinc  volatilizes 
and  the  earthy  substances  fuse  together  with  the  iron  slag.  After 
the  charge  has  become  cool,  the  button  consisting  of  brittle  matt 
and  slag  is  weighed,  and  its  weight  deducted  from  that  of  the 


ZINC — WET  ASSAYS.  209 

refractory  residue  of  the  zinc  blende  plus  3  grammes  iron  filings, 
plus  5  grammes  of  iron  slag.  The  difference  will  give  the  per- 
centage of  zinc.  The  fewer  the  metallic  impurities  in  the  blende, 
which  would  be  separated  by  the  iron  and  volatilized  (such  as 
antimony,  lead,  bismuth,  etc.),  the  more  accurate  will  this 
method  be. 

47.    WET  ASSAYS.1 

Gravimetric  and  volumetric  methods  are  used.  Although  the 
latter  assay  is  somewhat  less  accurate  than  the  former,  it  is 
nevertheless  available  in  many  cases  for  practical  purposes. 

A.   Gravimetric  assays. 

1.  Determination  of  zinc  as  zinc  sulphide. — 1  gramme  of  the 
finely  powdered  assay  sample,  previously  dried  at  100°  C. 
(212°  F.),  is  placed  in  a  long-necked  flask  and  dissolved  in  nitric 
acid.  Every  trace  of  nitrous  acid  is  removed  by  boiling,  and  the 
fluid  is  then  strongly  evaporated,  30  cubic  centimeters  of  nitric 
acid  and  about  200  cubic  centimeters  of  water  are  added,  and  the 
solution  is  then  precipitated  with  sulphuretted  hydrogen  without 
previous  filtration.  The  whole  is  now  filtered  off  (metallic  sul- 
phides, quartz,  etc.)  and  washed.  A  flask  is  now  placed  beneath 
the  funnel,  and  its  contents  are  treated  with  hot  nitric  acid  not  too 
concentrated.  The  filter  is  then  perforated,  the  undissolved  resi- 
due rinsed  off  into  the  flask,  and  the  filter  washed  out.  The  fluid 
is  strongly  reduced  by  boiling,  and  then  water  and  30  cubic  centi- 
meters of  nitric  acid  are  added.  It  is  again  precipitated  with 
sulphuretted  hydrogen,  filtered,  and  the  filtrate  which  carries 
some  zinc  is  added  to  the  principal  zinc  solution.  The  entire 
filtrate  is  then  boiled  nearly  to  dryness  in  the  long-necked  flask 
in  order  to  remove  the  sulphuretted  hydrogen,  some  potassium 
chlorate  being  added  for  the  higher  oxidation  of  any  ferrous 
oxide.  The  mass  is  then  supersaturated  with  pure  ammonia,  the 
iron  precipitate  filtered  off,  washed  and  dissolved  in  hot,  medium 
strong  nitric  acid.  It  is  now  again  precipitated  with  ammonia  to 
extract  any  residue  of  zinc,  and  filtered  through  the  same  filter, 
these  manipulations  being  repeated  once  or  twice  more.  The 

1  B.  u.  h.  Ztg.  1876,  pp.  148, 173  (Laur). 
14 


210  ASSAYING. 

entire  filtrate  is  now  acidulated  with  acetic  acid,  diluted  to  the 
volume  of  at  least  2  liters,  sulphuretted  hydrogen  is  introduced 
(in  the  absence  of  nickel  and  cobalt),  and  the  liquid  is  then 
allowed  to  stand  for  24  hours.  The  clear  liquid  is  then  poured 
off  upon  a  filter,  and  finally  the  zinc  sulphide.  The  flask  is 
rinsed  out  with  sulphuretted  hydrogen  water,  the  precipitate  is 
also  washed  with  it  with  the  addition  of  some  ammonium  acetate. 
The  filtrate  from  the  zinc  sulphide  is  supersaturated  with  ammo- 
nia and  allowed  to  stand  for  at  least  24  hours  in  a  covered  glass 
in  order  to  see  whether  any  zinc  sulphide  is  still  deposited.  The 
filter  is  dried,  and  the  zinc  sulphide  adhering  to  it  detached  by 
rubbing,  the  filter  being  entirely  closed  during  the  operation. 
The  zinc  sulphide,  together  with  the  ash  of  the  filter  and  some 
distilled  sulphur,  is  heated  in  one  of  Rose's  crucibles  (Fig.  70, 
p.  117)  until  it  commences  to  frit,  and  then  in  a  current  of  dry 
hydrogen  until  two  weighings  correspond  (ZnS  =  67.01  Zn).  The 
determination  of  zinc  as  zinc  sulphide  is  very  accurate. 

2.  Determination  of  zinc  as  zinc  oxide. — 1  gramme  of  ore  is 
dissolved  in  aqua  regia,  and  ammonia  in  excess  and  ammonium 
carbonate  are  added,  whereby  zinc  (and  copper)  passes  into  solu- 
tion. The  resulting  precipitate  (iron,  lead,  etc.)  is  again  dissolved 
and  precipitated,  and  ammonia  added  to  extract  any  remaining 
traces  of  zinc.  The  zinc  (and  copper)  is  then  precipitated  from 
the  filtrate  with  sodium  sulphide,  and  filtered.  The  zinc  sulphide 
is  separated  from  the  copper  sulphide  upon  the  filter  by  treating 
with  diluted  hydrochloric  acid,  and  the  copper  sulphide  remain- 
ing behind  is  washed.  The  zinc  is  precipitated  in  the  boiling 
filtrate  by  means  of  sodium  carbonate,  washed,  dried,  ignited, 
and  weighed  as  zinc  oxide  containing  80.24  per  cent,  of  zinc. 

The  zinc  may  also  be  precipitated  from  the  neutralized  filtrate 
from  the  copper  sulphide  by  means  of  sodium  sulphide,  and 
•determined  as  zinc  sulphide  (p.  209).  This  assay  is  less  accurate 
than  the  foregoing  one. 

-3.  Electrolytic  assay,  according  to  Beilstein  and  Jawein.1 — 0.5 

1  Liebig's  Jahresber.  1865,  p.  686  (Luckow)  ;  Fresenius's  Ztschr.  xv.  303 
•(Wrightson)  ;  xvi.  469  (Parodi  und  Masca/zini).  B.  u.  h.  Ztg.  1878,  p.  26 
•(Riche).  Ber.  d.  deutsch.  chem.  Ges.  1879,  No.  5,  p.  446  (Beilstein  und  Jawein). 


ZINC— WET   ASSAYS.  211 

to  1  gramme  of  ore  is  dissolved  in  nitric  or  sulphuric  acid,  and 
caustic  soda  added  until  a  precipitate  is  formed.  Solution  of 
potassium  cyanide  is  gradually  added  until  the  solution  becomes 
clear,  and  then  the  platinum  electrodes  (p.  Ill)  are  immersed  in 
the  solution.  The  current  of  4  Bunsen  elements  (the  cylinder  of 
zinc  15.5  centimeters  high,  the  carbon  dipping  into  nitric  acid, 
with  which  0.1  gramme  of  zinc  will  be  precipitated  per  hour)  is 
then  passed  through  the  liquid.  The  beaker-glass  containing  the 
solution  should  be  placed  in  a  dish  of  cold  water,  to  prevent  it, 
in  case  but  a  small  quantity  is  being  operated  on,  from  becoming 
strongly  heated  by  the  action  of  the  electric  current.  When 
precipitation  is  supposed  to  be  complete,  the  electrodes  are  lifted 
out  of  the  fluid,  the  zinc  is  first  washed  off  with  water,  next  with 
alcohol,  and  finally  with  ether,  and  then  dried  in  the  desiccator. 
After  being  weighed,  the  zinc  is  dissolved  from  the  platinum  with 
hydrochloric  or  nitric  acid,  and  the  electrodes  are  again  placed  in 
the  fluid  in  order  to  test  it  for  any  residual  zinc.  Black  stains, 
which  may  be  perceived  upon  the  electrodes,  after  the  zinc  has 
been  removed,  originate  from  finely  divided  platinum. 

When  copper  is  present  (as  for 'instance  with  brass),  the  sample 
is  dissolved  in  nitric  acid  and  evaporated  to  dryness.  The  residue 
is  taken  up  with  water,  and  the  copper  precipitated  by  electrolysis 
from  the  solution  previously  acidulated  with  nitric  acid,  when 
lead  will  be  deposited  on  the  platinum  spiral  as  peroxide.  The 
zinc  is  then  precipitated  as  above  described. 

According  to  Parodi  and  Mascazzini1  when  zinc  is  precipitated  from 
its  sulphate  solution,  the  quantity  of  zinc  in  this  solution  should 
not  be  over  0.10  to  0.25  gramme.  The  solution  should  be  mixed 
with  4  c.c.  of  ammonium  acetate,  2  c.c.  of  citric  acid,  and  diluted 
with  water  to  200  c.c.  The  electrodes  are  then  placed  in  position 
and  the  whole  covered  to  prevent  loss  by  sputtering.  A  current  of 
250  to  300  c.c.  of  oxyhydrogen  gas  per  hour  is  used.  The  separa- 
tion is  complete  when  a  sample  of  the  solution  no  longer  reacts 
with  potassium  ferrocyanide.  After  siphoning  off  the  solution, 
wash  precipitate,  interrupt  current,  and  again  wash  with  absolute 
alcohol,  and  dry  at  about  50°  C. 

*  Gaaa.  Chiro.  ital.  8.  Ztsclift.  f.  Anal.  Chem.     Bd.  18,  p.  587. 


212  ASSAYING. 

According  to  Rheinhardt  and  Ihle,1  the  solution  of  sulphate  or 
chloride  of  zinc,  which  should  be  as  neutral  as  possible,  is  mixed 
.with  an  excess  of  potassium  oxalate,  the  precipitate  of  zinc  oxalate 
is  dissolved  and  the  solution  electrolized.  The  oxalate  of  zinc  is 
decomposed  to  metallic  zinc  and  carbonic  acid,  and  the  potassium 
oxalate,  to  potassium  and  oxalic  acid.  The  potassium  acts  upon  the 
water  with  an  evolution  of  hydrogen  on  the  negative  pole,  at  the 
same  time  the  free  alkali  formed  is  converted  into  potassium  car- 
bonate by  the  carbonic  acid  at  the  positive  pole.  The  reaction  is 
nearly  complete  when  the  evolution  of  gas  at  the  positive  pole 
abates.  To  avoid  the  peculiar  stains  produced  by  electrically  de- 
po'sited  zinc  on  bright  platinum  it  is  well  to  previously  deposit  a 
slight  coating  of  copper  on  the  negative  electrode,  which  also  facili- 
tates the  recognition  of  the  end  of  the  precipitation.  The  coating 
of  copper  must,  however,  be  perfectly  bright ;  otherwise  the  zinc  will 
not  adhere  properly.  The  precipitated  zinc  is  bluish  white  and  ad- 
heres firmly  to  the  electrode.  The  precipitate  is  first  washed  with 
hot  water,  then  in  cold  water  free  from  air,  then  in  alcohol,  and 
finally  in  pure  ether  and  dried  in  a  desiccator.  The  precipitated  • 
zinc  is  redissolved  in  dilute  cold  HNO3,  the  layer  of  copper  is  but 
slightly  affected  and  reappears  with  a  bright  surface.  As  some  of 
the  copper  is  dissolved  with  the  zinc  it  is  useless  to  weigh  the  elec- 
trode freed  from  the  precipitate.  The  use  of  ammonium  oxalate 
instead  of  potassium  oxalate  is  not  recommended,  as  it  renders  the 
zinc  precipitate  somewhat  pulverulent  on  the  lower  edge  of  the 
electrode.  In  the  presence  of  sufficient  potassium  oxalate  the  pres- 
ence of  free  oxalic  acid  or  almost  any  other  acid  is  not  injurious, 
although  precipitation  takes  place  more  readily  from  a  neutral  solu- 
tion. The  presence  of  HN03  in  any  form  should  be  avoided,  as  it 
is  apt  to  cause  the  formation  of  ammoniacal  salts  which  prevent 
the  compact  precipitation  of  the  zinc.  As  the  potassium  carbonate 
formed  offers  a  strong  resistance  to  the  current,  it  is  recommended 
to  add  pure  neutral  potassium  sulphate  to  increase  the  conduc- 
tivity of  the  solution.  Moore2  states  that  from  a  H2S04  or  HC1 
solution  of  zinc  the  zinc  is  readily  precipitated  in  the  metallic  state 
with  a  current  of  5  c.c.  of  oxy hydrogen  gas  per  minute.  The  solu- 
tion must  contain  15  per  cent,  of  metaphosphoric  acid  and  heated 
to  70°  C.  with  the  addition  of  an  excess  of  ammonium  carbonate. 

1  Journ.  of  Pract.  Chem.  vol.  24,  p.  193. 
'  2  Chem.  News,  1886,  p.  219.     Chemikerztg,  1886,  p.  119. 


ZINC — WET   ASSAYS.  213 

By  adding  sodium  phosphate  to  a  potassium  cyanide  solution  and 
dissolving  the  phosphate  of  zinc  formed,  then  heating  to  80°  C. 
with  an  excess  of  ammonium  carbonate  and  using  a  current  of 
160  c.c.  of  oxy hydrogen  gas  per  hour,  the  zinc  is  precipitated  more 
rapidly  and  quite  as  completely.  It  is  claimed,  in  this  connection, 
that  the  zinc  deposits  better  upon  a  silver-plated  electrode. 

According  to  Millot,1  the  electrolytic  determination  of  zinc  in  ores 
is  easily  effected  by  the  following  method  : — 

Dissolve  2.5  grammes  of  the  ore  in  50  c.c.  of  HC1,  add  potassium 
chlorate  to  oxidize  the  iron  and  evaporate  to  dryness  to  separate 
the  silica.  Take  up  with  water  and  precipitate  the  lime  and  lead 
with  100  c.c.  of  ammonia  and  5  c.c.  of  ammonium  carbonate, 
filter,  dilute  to  1  liter  and  mix  this  solution  with  a  solution  of  1 
gramme  of  KG  Y  in  100  c.c.  of  water.  Place  electrode  in  this  solu- 
tion and  pass  current  through.  The  electrodes  should  not  be  more 
than  a  few  millimeters  apart.  A  current  from  two  Bunsen  cells 
will  finish  the  precipitation  in  nine  or  ten  hours.  The  precipitated 
zinc  adheres  tightly  and  can  be  readily  washed. 

According  to  Classen,  a  H2S04  solution  containing  about  0.1 
gramme  of  zinc  is  concentrated  to  about  50  c.c.,  the  free  acid  neu- 
tralized with  caustic  potash,  excess  of  ammonium  oxalate  added, 
the  solution  heated  and  3  or  4  grammes  of  solid  ammonium  oxalate 
dissolved  in  it,  and  the  hot  solution  subjected  to  the  current  of  two 
Bunsen  cells.  The  zinc  separates  very  easily  as  a  bluish  or  gray 
white  coating  on  the  negative  electrode.  The  precipitation  is  com- 
plete when  no  more  gas  is  developed  on  the  positive  electrode,  and 
a  sample  of  the  solution  shows  no  zinc  reaction  with  ammonium 
sulphide.  The  precipitated  zinc  dissolves  with  difficulty  in  acids ; 
there  generally  remains  a  dark  coating  on  the  platinum  electrode, 
which  can  only  be  removed  by  igniting  and  repeated  treatment 
with  acids.  The  use  of  HNO,  for  dissolving  the  ore  is  not  advis- 
able, as  its  presence,  or  even  that  of  a  nitrate,  hinders  the  separation 
of  the  zinc  in  a  compact  form. 

In  the  electrolytic  determination  of  zinc  from  a  slightly  acid  so- 
lution in  the  presence  of  a  strong  mineral  acid,  Luckow2  recom- 
mends first  placing  in  the  platinum  dish,  used  as  an  electrode, 
about  0.5  to  O.f  gramme  of  mercury.  The  platinum  dish  and  its 
contents  are  then  weighed,  after  which  the  solution  to  be  decom- 

1  Soc.  Chim.     Paris,  1882,  p.  339.     Chemikerztg,  1882,  p.  410. 

2  Chemikerztg,  1885,  p.  338. 


214  ASSAYING. 

posed  (containing  from  0.10  to  0.15  gramme  zinc)  is  placed  in  it.  A 
platinum  spiral  is  used  as  the  positive  pole  and  the  dish  as  the  nega- 
tive. A  current  of  120  to  150  c.c.  of  oxy hydrogen  gas  per  hour 
from  6  to  8  Meidinger  cells  is  used.  When  the  zinc  separates  it  forms 
an  amalgam  which  coats  the  inside  of  the  dish.  When  the  precipita- 
tion is  complete  the  amalgam  is  washed  with  water  and  alcohol, 
dried,  and  the  dish  again  weighed.  Platinum,  iron,  nickel,  cobalt, 
and  manganese  do  not  form  an  amalgam  with  mercury  in  this 
manner ;  consequently  this  method  can  be  used  in  the  separation,  of 
zinc  from  these  metals.  This  method  is  also  very  useful  in  the 
electrolytic  determination  of  silver. 

B.  Volumetric  assays. — Of  the  volumetric  assays  which  have 
been  recommended — 

1.  Schqffner's  assay  with  sodium  sulphide1  is  used  more  than 
any  other.  This  is  based*  upon  the  precipitation  of  zinc  from 
ammoniacal  solution  by  means  of  sodium  sulphide.  The  termina- 
tion of  precipitation  is  indicated  by  the  blackening  of  ferric 
hydrate  as  below  described.  This  assay,  if  certain  precautionary 
measures  are  adopted,  allows  of  a  determination  of  the  zinc  to 
within  0.5  per  cent.  The  presence  of  metals  soluble  in  ammonia 
(copper  and  manganese  ;  nickel  and  cobalt  occur  but  seldom)  re- 
quires modifications  of  the  method. 

0.5  gramme  of  oxidized  ores  (smithsonite,  calamine),  with  over 
35  per  cent,  of  zinc,  and  more  if  the  ore  is  poorer,  are  dissolved 
in  heated  hydrochloric  acid,  with  an  addition  of  a  few  drops  of 
nitric  acid,  to  oxidize  the  iron ;  the  solution  is  then  supersaturated 
with  ammonia:  or,  raw,  or  roasted  zinc  blende  is  dissolved  in 
aqua  regia,  evaporated  to  dryness,  and  the  residue  dissolved  in  5 
cubic  centimeters  of  hydrochloric  acid  and  some  water.  Copper 
(also  lead,  antimony,  etc.)  being  frequently  present,  the  solution 
is  precipitated  with  sulphuretted  hydrogen,  filtered,  and  the  gas 
driven  off  by  boiling.  10  cubic  centimeters  of  aqua  regia  are 

1  B.  u.  h,  Ztg.  1856,  p.  231,  306;  1857,  p.  60  (Schaffner)  ;  1876,  p.  148, 
174  (Laur)  ;  p.  225  (Thum)  ;  p.  304  (Tobler).  Journ.  f.  prakf.  Chem. 
Ixxxviii.  486  (Kiintzel).  Fresenius's  Ztschr.  1870,  p.  465  (Deus)  ;  1871,  p. 
209  (Schott).  Mohr,  Titrirmethode,  1874,  p.  466  (F.  Mohr).  Dingier,  cxlviii. 
115  (C.  Mohr).  Preuss.  Ztschr.  Bd.  25  (Hampe).  Berggeist,  1874,  No.  3 
(Allenberger  Pr.).  Berichte  der  deutsch.  chein.  Ges.  1879,  No.  3,  p.  270 
(Aarland).  Percy's  Metallurgy.  Copper,  Zinc,  and  Brass,  p.  598. 


ZINC — WET   ASSAYS.  215 

added  (or  some  chlorine  water,  or  a  few  drops  of  bromine  may  be 
added  to  the  acid  solution,  or  potassium  permanganate  to  faint 
reddish  coloration  to  the  ammoniacal  solution,  and  allowing  it  to 
stand  for  one  hour)  for  the  higher  oxidation  of  the  iron  and 
manganese  (if  iron  alone  is  present,  an  addition  of  nitric  acid  or 
potassium  chlorate  suffices),  which,  when  ammonia  in  excess  is 
added,  are  precipitated  as  hydrated  oxides,  while  the  zinc  remains 
in  solution.  The  hydrated  oxides  are  again  dissolved  in  hydro- 
chloric acid  and  precipitated  with  ammonia  in  excess,  in  order  to 
extract  any  residue  of  zinc.  Both  nitrates  are  then  united  and 
diluted  (to  500  cubic  centimeters  if  5  grammes,  and  to  175  to  225 
cubic  centimeters  if  0.5  gramme  of  ore  have  been  used).  50  cubic 
centimeters  of  the  fluid  are  then  placed  in  a  beaker-glass,  1  to  2 
drops  of  a  solution  of  ferric  chloride  of  the  concentration  given 
below  are  dropped  into  1  cubic  centimeter  of  ammonia  contained 
in  a  porcelain  saucer.  The  precipitated  hydrated  ferric  oxide  is 
carefully  rinsed  in  the  beaker-glass,  where  it  settles  on  the  bottom. 
Titrated  solution  of  sodium  sulphide  (1  cubic  centimeter  «  0.008  to 
0.009  gramme  of  zinc)  is  then  added,  the  contents  of  the  beaker-glass 
being  given  a  spiral  motion  in  the  meanwhile,  so  that  the  flakes 
remain  on  the  bottom.  The  addition  of  the  sodium  sulphide  is 
continued  until  the  flakes  of  ferric  oxide  become  discolored,  and 
finally  assume  a  brown  color,  which  indicates  that  all  the  zinc  has 
been  precipitated.1 

The  following  have  also  been  recommended  as  indicators  for 
recognizing  the  final  reaction ;  though  none  of  them  have  taken  the 
place  of  the  hydrated  ferric  oxide.  Porcelain  saturated  with 
ferric  chloride  (Barreswill),  or  paper  (Streng)  which  is  weighted 
with  platinum  wire  and  laid  upon  the  bottom  of  the  beaker- 
glass  ;  drop  samples  ( Tupfproberi)  with  nickel  chloride  (Kuntzel), 
cobaltous  chloride  (Deus),  alkaline  solution  of  lead  tartrate 
(F.  Mohr) ;  blotting-paper  saturated  with  sugar  of  lead,  and  then 
treated  with  ammonium  carbonate  (Fresenius) ;  nitro-prussiate  of 
sodium  ( C.  Mohr)  •  sized  paper  coated  with  white  lead,  so-called 

1  It  is  advisable  to  have  a  stand  with  three  burettes  respectively  for  solution 
of  zinc,  sodium  sulphide,  and  ferric  chloride. 


216  ASSAYING. 

"  polka"  paper  (Schott),  over  which  filtered  drops  of  the  fluid  are 
allowed  to  run. 

The  following  points  must  be  observed  in  order  to  make  the 
assay  successful. 

a.  The  quantity  of  the  hydrated  ferric  oxide,  which  is  added, 
must  not  vary  too  much,  and  must  possess  a  uniform  coherence. 
This  may  be  produced  by  dissolving  3  grammes  of  piano  wire  in 
aqua  regia,  and  diluting  this  to  a  bulk  of  100  cubic  centimeters. 
The  same  number  of  drops  of  this  solution  are  allowed  to  fall 
each  time,  for  instance  from  a  burette,  into  1  cubic  centimeter  of 
concentrated  ammonia  (p.  215).     The  ring-like  clot  of  hydrated 
ferric  oxide  which  will  be  formed  in  about  one  minute  may  then 
be  rinsed  into  the  fluid  which  is  to  be  titrated. 

b.  The  same  shade  of  coloration  of  the  hydrated  ferric  oxide 
used  in  the  operation  should  always  be  taken  as  closely  as  possi- 
ble to  indicate  the  end  of  the  reaction,  as  the  quantities  of  sodium 
sulphide  consumed  in  producing  various  shades  vary  considerably. 

c.  The  quantity  of  fluid,  into  which  the  added  excess  of  sodium 
sulphide  is  divided  in  titrating,  exerts  a  material  influence  in 
respect  to  its  action  upon  the  hydrated  ferric  oxide,  as,  when  the 
quantity  of  fluid  becomes  smaller,  a  smaller  excess  of  sodium 
sulphide  suffices  for  blackening  the  hydrated  ferric  oxide. 

In  consideration  of  this  circumstance,  the  volume  of  liquid  is 
measured,  according  to  Tobler,  in  the  smelting  works  of  the 
Vieille  Montagne,  at  the  termination  of  the  titration,  and  for  each 
100  cubic  centimeters  of  it,  the  volume  of  sodium  sulphide  con- 
sumed is  decreased  0.7  and  0.5  cubic  centimeters,  its  standard 
being  0.008  to  0.009  gramme  of  zinc  to  1  cubic  centimeter.  Ac- 
cording to  Thum,  this  correction  can  be  avoided,  -by  always 
bringing  all  the  liquids  before  titration  to  an  equal  volume,  and 
by  using  so  much  zinc  for  standardizing  as  corresponds  to  the 
average  percentage,  and  the  quantity  of  zinc  ore  used.  This 
zinc  is  dissolved  and  the  solution  diluted  to  a  volume  equal  to 
that  of  the  solution  of  the  ore,  and  the  titer  of  this  is  taken. 
Under  these  conditions  there  can  be  no  material  difference  in  the 
quantities  of  sodium  sulphide  consumed  in  fixing  the  standard 
of  the  solution  and  of  those  consumed  in  the  analysis,  and 
therefore  the  quantities  of  liquid  must  be  nearly  equal  after  the 


ZINC — WET   ASSAYS.  217 

titration,  and   in  consequence  of  this   no  errors   can  occur  on 
account  of  differences  of  volumes. 

d.  It  does  not  make  any  difference,  as  far  as  the  accuracy  of 
the  assay  is  concerned,  whether  the  hydrated  ferric  oxide  is  intro- 
duced at  the  commencement,  or  towards  the  end  of  the  titration, 
if  the  same  order  is  always  observed.     The  heating  of  the  liquid 
exerts  also  but  little  influence. 

e.  Admixtures  having  a  disturbing   effect  must  be  removed. 
Copper,  silver,  cadmium,  cobalt,  nickel  chromium,  manganese,  ar- 
senic, and  antimony  are  soluble  in  ammonia,  and  also  lead  in  small 
quantities,  which  last,  after  the  precipitation  with  ammonia,  may 
be  present  either  as  carbonate,  sulphate,  and  basic  chloride,  or  as 
oxy-salt.     Of  these,  the  last  two  are  the  more  soluble  in  ammonia. 
Copper,  lead,  manganese,  and  iron  occur  most  frequently. 

Copper,  together  with  cadmium,  silver,  arsenic,  and  antimony, 
is  removed  by  sulphuretted  hydrogen.  If  a  small  quantity  only 
is  present,  it  can  be  determined  by  Heine's  colorimetric  assay,  and 
titrated  with  sodium  sulphide,  notwithstanding  the  blue  coloring 
of  the  ammoniacal  zinc  solution,  and  the  total  consumption  of 
sodium  sulphide,  reduced  by  the  volume  corresponding  to  the 
percentage  of  copper  found.  Manganese  is  the  least  injurious  of 
all,  and  can  be  easily  removed  as  above  described,  p.  215.  It 
becomes  sulphurized  later  than  the  hydrated  ferric  oxide,  and  the 
percentage  of  zinc  can  be  accurately  determined  by  taking  the 
commencement  of  the  blackening  of  the  hydrated  ferric  oxide  as 
indicator  of  the  final  reaction,  and  not  continuing  until  it  has 
turned  entirely  black.  But  it  is  best  to  first  remove  the  manga- 
nese by  precipitation  in  case  a  considerable  percentage  of  it  is 
present.  This  fact  may  be  recognized  by  a  concentrated  acid 
solution,  notably  losing  its  original  dark  color,  upon  dilution. 
Lead  is  removed  by  sulphuretted  hydrogen  with  the  copper,  or  by 
evaporating  the  substance  to  dryness  with  sulphuric  acid,  after 
the  preliminary  treatment  with  acids,  then  taking  up  with  diluted 
sulphuric  acid,  and  removing  the  lead  sulphate  by  filtration,  etc. 
When  more  than  5  per  cent,  of  iron  is  present,  the  ammoniacal 
precipitate  must  always  be  redissolved  at  least  once.  Organic 
substances,  which  are  sometimes  found  in  foreign  zinc  ores,  are 
destroyed  by  heating  to  redness  with  free  access  of  air,  as  other- 


218  ASSAYING. 

wise  they  might  easily  reduce  the  ferric  oxide  to  ferrous  oxide, 
which  is  soluble  to  some  extent  in  ammonia,  and  decomposes 
sodium  sulphide. 

/.  The  zinc  used  for  fixing  the  standard  solution  must  be  suffi- 
ciently pure. 

Good  commercial  zinc  is  purified  by  smelting  50  grammes 
4n  a  porcelain  crucible  over  a  lamp ;  keeping  it  in  this  state 
for  a  quarter  of  an  hour,  poling  it  with  a  wooden  stick.  The 
layer  of  oxide  is  then  taken  off,  and,  after  the  metal  has 
stood  for  a  few  minutes,  one-half  of  it  is  poured  into  another 
crucible,  where  the  same  operation  is  repeated.  Half  of  the 
metal  is  again  poured  off,  these  manipulations  being  repeated 
several  times.  The  zinc  is  then  dropped  upon  a  cold  zinc  plate 
(the  surface  of  which  must  be  free  from  oxide)  so  that  each  drop 
forms  a  small  thin  disk  that  may  be  readily  broken  to  fragments. 
It  should  be  kept  under  a  bell-glass  with  calcium  chloride.  The 
American  Passaic  zinc  is  very  pure. 

g.  There  should  be  a  uniform  light  in  the  room  during  the 
titration,  so  as  to  enable  the  operator  to  observe  correctly  the 
coloring  of  the  iron.  This  is  best  arranged  by  covering  the 
windows  with  tracing  linen  or  tissue  paper  (Altenberg). 

2.  Assay  with  potassium  ferrocyanide.1 — The  zinc  is  precipi- 
tated from  an  acid  solution  by  potassium  ferrocyanide,  uranic 
salt  being  used  as  an  indicator.  When  all  the  zinc  is  precipi- 
tated, the  uranium  salt  produces  a  brownish  stain,  when  a  test 
is  made  by  taking  a  drop  upon  a  white  plate.  5  grammes  of 
ore  are  dissolved  in  aqua  regia,  and  evaporated.  Hydrochloric 
acid  in  excess  is  added  to  the  residue,  the  copper,  etc.,  are  pre- 
cipitated with  sulphuretted  hydrogen  and  filtrated.  The  filtrate 
is  boiled,  the  ferrous  oxide  is  oxidized  by  potassium  chlorate,  and 
ammonia  is  added.  The  ferric  oxide  and  alumina  are  then 
filtered,  and  again  dissolved  and  precipitated.  The  filtrate  is 
neutralized  with  hydrochloric  acid  and  an  additional  10  to  15 
cubic  centimeters  of  hydrochloric  acid  of  1.12  specific  gravity  are 
added.  The  solution  is  then  titrated  with  the  solution  of  potas- 

1  Dingier,  cxcv.  260  (Galletti)  ;  Fresenius's  Ztschr.  1875,  pp.  189,  343 
(Lyte  and  Galletti)  ;  1874,  379  (Fahlberg)  ;  Dingier,  cxc.  229  (Renard)  ;  cxc. 
395  (Reindl). 


ZINO — WET   ASSAYS.  219 

slum  ferrocyanide  (1  cubic  centimeter) =0.01  gramme  of  zinc  until 
the  appearance  of  the  first  brownish  stain  by  the  drop  test  with 
solution  of  uranic  salt. 

In  determining  zinc  with  potassium  ferrocyanide  the  presence  of 
manganese  exerts,  according  to  Galetti,  an  injurious  influence,  as  it  is 
precipitated  with  the  zinc.  It  is,  therefore,  recommended  by  Mason,1 
after  the  separation  of  the  metals  precipitated  by  H2S,  to  acidulate 
the  solution  with  acetic  acid  and  treat  it  with  H2S.  Dissolve  the 
washed  precipitate  of  sulphide  of  zinc  in  HC1,  and  use  this  solution 
alone  for  titration.  According  to  Giudice,2  in  the  presence  of  tartaric 
acid  the  zinc  alone  is  precipitated  from  an  ammoniacal  solution  by 
potassium  ferrocyanide,  whilst  the  iron,  lead,  and  alumina  remain 
in  solution,  thus  rendering  the  separation  of  the  zinc  from  these 
metals  unnecessary.  Copper  and  manganese,  however,  must  not 
be  present.  A  ferric  salt  is  used  as  an  indicator  ;  when  it  is 
brought  in  contact  with  a  drop  of  the  solution  acidulated  with  acetic 
acid,  the  ferrocyanide  of  zinc  is  not  affected  by  the  acetic  acid. 

Dissolve  0.5  to  1.0  gramme  of  the  ore  in  HN03  or  HN03+HC1, 
dilute  to  three  times  the  volume  of  solution,  and  add  potassium 
ammonium  tartrate.  Add  excess  of  ammonia  and  dilute  to  300  or 
400  c.c.  Although  usually  the  solution  is  not  entirely  clear,  filter- 
ing is  not  necessary.  The  titer  is  best  set  for  a  solution  of  pure 
zinc,  or  of  a  pure  zinc  salt  of  known  metallic  content.  Galletti's 
titrating  solution  may  also  be  used. 

Determination  of  zinc  by  decomposing  the  sulphide  of  zinc  with 
chloride  of  silver,  and  determining  the  zinc  from  the  equivalent 
content  of  chlorine,  according  to  Mann.3 — Dissolve  1  gramme  of  the 
assay  material  in  HN03,  pass  H2S  through  solution,  filter,  boil  the 
filtrate  and  precipitate  the  ferric  oxide  and  alumina  with  ammonia, 
redissolving,  however,  the  larger  part  of  this  precipitate  in  HN03, 
and  again  precipitating.  Add  to  the  two  filtrates,  which  contain 
zinc  and  some  manganese,  acetic  acid,  and  again  pass  H2S  through. 
Boil  oft7  excess  of  H2S,  filter  while  hot,  and  place  the  filter  with  the 
.sulphide  of  zinc  in  a  small  beaker,  add  30  to  50  c.c.  of  hot  water, 
stir  with  glass  rod,  and  add  an  excess  of  thoroughly  pure  moist 
chloride  of  silver,  which  should  be  kept  on  hand  protected  from  the 

1  Am.  Chem.  Jour.  vol.  4,  p.  53.     Ztschft.  f.  anal.  Chem.  Bd.  22,  p.  246. 

2  Giorn.  Farm.  Chem.  31,  p.  337.     Cheraikerztg,  1882,  p.  1034. 

8  Oesterr.  Ztschft.  f.  Bg.  u.  Httnwsn.  1879,  p.  426.  Ztschft.  f.  anal.  Chem. 
Bd.  18,  p.  162. 


220  ASSAYING. 

light.  Boil  until  the  sulphide  of  zinc  is  entirely  decomposed,  and 
the  supernatant  liquid  perfectly  clear,  then  add  a  few  drops  of  dilute 
(1:6)  H2S04,  filter  and  wash  cold.  The  filtrate  contains  all  the 
zinc  as  chloride.  Now  add  an  excess  of  nitrate  of  silver,  shake 
well,  and  mix  with  a  few  c.c.  of  iron-ammonium-alum,  or  ferric 
sulphate,  and  determine  excess  of  silver  by  Yolhard's  method,  by 
which  the  amount  of  silver  not  precipitated  by  the  chlorine  is  de- 
termined. From  the  amount  of  silver  precipitated  by  the  chlorine 
the  content  of  zinc  is  calculated. 

Preparation  of  the  titrating  solutions. — Dissolve  33.2  grammes 
of  pure  silver  in  HN03,  evaporate  to  dryness,  take  up  with  water, 
and  dilute  to  1  liter.  One  c.c.  of  this  solution  contains  0.0332 
gramme  of  silver,  and  corresponds  to  0.01  gramme  of  zinc.  The 
standard  solution  of  sulpho-cyanide  is  prepared  so  that  1  c.c.  ex- 
actly equals  1  c.c.  of  the  silver  solution. 

Determination  of  zinc  from  its  combinations  with  sulphur  by 
decomposition  with  nitrate  of  silver.  Balling's  method.1 — The 
pure  sulphide  of  zinc,  obtained  by  separation  from  the  other  metals 
by  the  wet  method,  is  filtered  off,  thoroughly  washed  from  the  filter 
into  a  beaker,  and  an  excess  of  nitrate  of  silver  poured  over  it — the 
amount  of  silver  present  must  be  in  excess.  The  whole  is  boiled 
for  about  a  half  hour.  Since  216  of  silver  correspond  to  65.2  of 
zinc,  at  least  (6^j=)  3.312  centigrammes  of  silver  must  be  added  for 
every  centigramme  of  zinc  expected.  The  decomposition  of  the  sul- 
phide of  zinc  and  nitrate  of  silver  is  plainly  perceptible  at  ordinary 
temperatures,  and  at  a  boiling  heat  it  is  effected  in  a  half  hour. 
Filter  off  the  sulphide  of  silver,  wash  the  filter,  and  place  it  and  its 
contents  in  a  flask  containing  boiling  HN03  of  1.2  sp.  gr.  Boil  until 
no  more  brown  vapors  escape,  dilute  with  water,  and,  after  cooling, 
titrate  with  ammonium  sulpho-cyanide.  Use  the  normal  silver  so- 
lution prepared  for  Yolhard's  silver  assay,  and  the  corresponding 
solution  of  ammonium  sulpho-cyanide  (see  page  155)  as  the  titrat- 
ing solutions.  Since  the  zinc  is  determined  by  the  quantity  of 
silver  equivalent  to  it,  each  c.c.  of  the  cyanide  salt  used  in  titrating 
has  to  be  multiplied  by  0.30185  to  get  the  content  in  the  assay  ma- 
terial. This  method  is  well  adapted  for  the  determination  of  lead 
and  copper  in  their  sulphur  combinations,  and  still  better  for  the 

1  Oesterr.  Ztschft.  f.  Bg.  u.  Httnwsn.  1881,  p.  35.  Ztschft.  f.  anal.  Chem. 
Bd.  22,  p.  250. 


ZINC — WET   ASSAYS.  221 

separation  of  these  metals,   as  they  can  be  determined  one   after 
another  with  the  same  re-agent. 

Determination  of  lead,  copper,  and  zinc  in  one  solution,  accord- 
ing to  this  method. — These  three  metals  are  frequently  associated  in 
alloys,  and  are  first  conjointly  precipitated  from  an  acetic  acid 
solution.  The  associated  metallic  sulphides  are  filtered  off  and  de- 
composed with  nitrate  of  silver,  the  silver  sulphide  formed  by 
titrating  with  ammonium  sulpho-cyanide,  corresponds  to  the  sul- 
phides of  the  three  metals  dissolved.  The  filtrate  from  the  silver 
sulphide  again  contains  the  three  metals.  After  precipitating  the 
excess  of  silver  with  HC1,  and  separating  the  lead  with  H2S04, 
neutralize  the  slightly  acid  solution  with  soda,  until  somewhat 
turbid,  then  add  acetic  acid  until  the  liquid  becomes  clear.  Precipi- 
tate the  copper  and  zinc  with  H2S,  filter,  wash,  and  again  decom- 
pose with  nitrate  of  silver.  The  difference  between  the  amounts  of 
nitrate  of  silver  used  in  the  first  and  second  titrations,  corresponds 
to  the  amount  of  lead  present.  The  excess  of  silver  is  separated,  as 
before,  with  HC1,  and  after  filtering  it  off  the  copper  is  precipitated 
with  H2S,  and  determined  separately  in  the  same  manner.  The 
amount  used  in  the  third  titration  corresponds, to  the  copper,  and 
by  adding  it  to  the  difference  first  found,  which  corresponds  to  the 
lead,  and  subtracting  the  total  from  the  total  consumption  of  sulpho- 
cyanide  used  in  the  first  titration,  we  have  the  amount  of  silver 
which  corresponds  to  the  zinc.  Should  silver  be  present  in  the  sub- 
stance assayed,  it  is  determined  in  the  beginning  from  the  HN03- 
solution  with  ammonium  sulpho-cyanide,  the  silver  cyanide  is 
filtered  off,  the  other  metals  remaining  in  solution  in  the  filtrate. 
In  calculating  the  amount  of  lead,  the  number  of  c.c.  of  sulpho- 
cyanide  used  is  multiplied  by  0.95833,  and  for  the  copper  the  num- 
.  ber  of  c.c.  of  sulpho-cyanide  is  multiplied  by  0.29351. 

3.  Schober's  volumetric  assay.1 — The  zinc  is  precipitated  with 
an  alkaline  sulphide  solution.  The  excess  of  sulphide  used  is  de- 
composed with  silver  solution,  and  finally  the  quantity  of  the 
solution  of  silver,  which  has  been  added  in  excess  and  remained 
undecomposed,  is  determined  by  ammonium  sulpho-cyanide  ac- 
cording to  Volhard's  method  (p.  155). 

1  Oesterr.  Ztschr.  1879,  5. 


222  ASSAYING. 

IX,  CADMIUM, 

48.    ORES. 

It  occurs  more  seldom  as  an  ore  (greenockite,  CdS,  with  77.6 
Cd)  than  as  a  constituent  of  calamine  and  zinc  blende. 

49.    ELECTROLYTIC   ASSAY.1 

Cadmium  sulphide  is  precipitated  from  an  acid  solution  with 
sulphuretted  hydrogen.  This  (and  also  cadmium  oxide)  is  dis- 
solved in  nitric  acid,  the  free  acid  is  neutralized  with  caustic 
potassa,  with  an  addition  of  potassium  cyanide  solution,  until  the 
precipitate  is  dissolved.  It  is  then  diluted  with  a  sufficient  quan- 
tity of  water,  so  that  about  0.2  gramme  of  cadmium  is  contained 
in  75  cubic  centimeters  of  the  liquid.  The  cadmium  is  then  pre- 
cipitated upon  the  platinum  cone  (p.  Ill)  with  3  Bunsen  elements, 
the  glass  containing  the  liquid  being  placed  in  a  dish  filled  with 
cold  water.  The  rate  of  precipitation  should  be  from  80  to  90 
milligrammes  of  metal  per  hour.  The  light  gray  cadmium  is 
rinsed  off  with  water,  then  with  alcohol,  and  dried  by  placing  it 
in  a  heated  platinum  dish  (p.  112). 

According  to  Clark,2  from  an  ammoniacal  solution  cadmium  is 
precipitated  in  a  spongy  porous  condition  containing  impurities  so 
that  the  results  are  too  high.  From  neutral  acetic  acid  solutions 
with  a  strong  current  cadmium  is  precipitated  in  a  crystalline  form 
suitable  for  weighing.3 

According  to  Yver,4  zinc  and  cadmium  can  be  separated  by  electro- 
lysis if  the  solution  containing  both  metals  as  sulphates  or  acetates 
is  mixed  with  2  or  3  grammes  of  sodium  acetate  and  a  few  drops  of 
acetic  acid.  The  cadmium  alone  is  separated  in  a  crystalline  form 
on  the  negative  pole.  With  two  Daniell  cells,  0.18  to  0.21  gramme 
of  cadmium  can  be  precipitated  in  3  or  4  hours.  The  zinc  remains 
behind  in  solution. 

1  Berichte  der  deutsch.  Chem.    Ges.  1879,  No.  vii.  p.  759. 

2  Am.  .Tourn.  of  Science  and  Arts,  vol.  16,  p.  200. 

3  Berichte  d.  deutsch.  Chem.     Ges.     Bd.  11,  p.  2048. 

4  Bulletin  de  la  Societ4  Chemique,  vol.  34,  p.  18. 


DETERMINATION   OF   TINSTONE   BY   WASHING.  223 

According  to  Classen,  cadmium  may  be  precipitated  completely 
from  solutions  of  ammonium  or  potassium  double  oxalate,  preferably 
the  latter.  The  solution  is  treated  with  an  excess  of  ammonium  or 
potassium  oxalate  diluted  to  200  c.c.,  and  electrolyzed  hot.  Care 
must  be  taken  that  the  volume  of  the  solution  is  not  reduced  by 
evaporation.  The  end  of  the  reaction  is  shown  by  testing  with 
hydrogen  sulphide. 

According  to  Beilstein  and  Jawein,  cadmium  may  be  determined 
in  the  same  way  as  zinc.  If  the  solution  contains  free  acid,  it  is 
neutralized  with  potassium  hydroxide,  and  potassium  cyanide  added 
till  the  solution  becomes  clear.  A  current  from  three  Bunsen  cells 
is  used,  and  the  solution  diluted  so  that  0.2  gramme- of  cadmium 
is  contained  in  15  c.c.  The  vessel  in  which  the  reaction  takes 
place  is  cooled  during  the  process. 


X,  TIN, 

50.    ORES. 

Tinstone  (cassiterite\  SnO2,  with  78.7  per  cent.  tin. 

51.    DETERMINATION    OF    TINSTONE   BY   WASHING. 

This  method  is  used  for  testing  borings  from  mines,  in  order 
to  ascertain  whether  poor  tin  iron  ores  are  worth  working  (Sax- 
ony) ;  or  in  concentrating  works,  to  determine  the  quantity  of 
material  worth  smelting  which  may  be  obtained  from  an  ore- 
heap  (Cornwall).  The  specific  gravity  of  tinstone  =  6.8  to  7.0. 

A.  Saxon  assay  of  tin.  —  A  sample  of  dust,  taken  by  volume,  is 
washed  in  the  vanning  trough. 

E.  Determination  of  tin  by  washing  in  Cornwall}  —  50  kilo- 
grammes of  samples  are  taken  from  different  parts  of  the  heap. 
The  mass  is  comminuted  and  thoroughly  mixed.  From  this, 
another  sample  is  taken,  sifted,  and  dried,  and  55  to  56  grammes 
of  it  are  weighed  off.  This  is  placed  upon  an  iron  shovel,  and 
washed,  by  imparting  to  it,  first  a  rotary  motion,  and  then  a 
decided  upward  and  downward  movement.  By  these  operations, 


B. 


u.  h.  Ztg.  1859,  p.  358.     Muspratt's  Chemie,  vii.  1375. 


224  ASSAYING. 

the  products  free  from  tin  will  be  washed  away,  while  those 
yielding  tin  will,  according  to  their  specific  gravity,  be  collected 
on  different  parts  of  the  shovel.  They  are  then  removed,  and,  if 
necessary,  roasted,  and  again  washed.  This  manipulation  requires 
considerable  skill  (see  p.  28). 

52.    FIRE  ASSAYS. 

The  object  of  these  is  to  reduce  the  tin  oxide  (stannic  acid)  and 
slag  off  the  admixtures  of  earths  by  solvent  fluxes.  The  accuracy 
of  the  result  .is  impaired,  or  the  assay  is  made  difficult,  on  account 
of  the  tin  oxide  being  easily  slagged  off  by  acids  and  bases ;  by 
the  difficulty  of  uniting  the  reduced  particles  of  tin  to  a  single 
button ;  and  by  the  presence  of  many  foreign  metallic  combina- 
tions and  earths  which  promote  the  slagging  off  or  the  contami- 
nation of  the  tin. 

The  losses  by  the  German  method  are  less  than  by  the  English 
or  Cornish  method.  The  assay  with  potassium  cyanide  gives  the 
highest  yield.  The  tin  buttons  obtained  by  the  fire  assay  must 
be  tested  in  the  wet  way  for  the  presence  of  copper,  iron,  etc., 
by  treating  them  with  nitric  acid  of  1.3  specific  gravity,  adding 
water,  digesting,  filtering,  drying,  igniting,  and  weighing  the  tin 
oxide. 

A.  German  assay. — 5  grammes  of  clean  ore  are  intimately 
rubbed  together  with  0.75  to  1  gramme  of  powdered  charcoal. 
The  mixture  is  poured  into  a  suitable  crucible  (Fig.  52,  p.  65), 
and  covered  with  12.5  to  15  grammes  of  carbonaceous  black  flux 
or  potash  with  50  per  cent,  of  flour,  1  to  1.25  grammes  of  borax 
glass,  and  finally  with  a  cover  of  common  salt  and  a -small  piece 
of  coal.  The  charge  is  exposed  for  three-quarters  to  one  hour  to 
a  very  strong  red  heat  in  the  reverberatory  (p.  54)  or  muffle- 
furnace  (p.  45),  or  for  one-half  to  three-quarters  of  an  hour  in  the 
blast  furnace  (p.  59).  The  crucible  is  then  taken  out  and  allowed 
to  become  entirely  cold,  as  tin  has  a  low  fusing  point.  It  is  then 
freed  from  slag,  and  the  result  must  be  a  single,  ductile  button  of 
a  tin-white  color,  which  does  not  follow  the  magnet  under  water 
In  case  the  tin  is  distributed  in  the  slag,  this  must  be  washed  off 
and  the  metal  collected. 


TIN — FIRE   ASSAYS.  225 

Other  charges :  25  grammes  of  ore,  5  grammes  of  argol,  20 
grammes  of  soda,  and  3  grammes  of  lime,  are  intimately  mixed 
together,  and  covered  with  a  layer  of  soda  and  10  grammes  of 
borax.  The  charge  is  smelted  at  a  strong  red  heat  and  kept  in 
fusion  for  twenty  minutes.  Or  for  siliceous  ores :  10  grammes 
of  ore,  and  from  10  to  20  grammes  of  fluor-spar  or  cryolite  are 
placed  in  a  charcoal-lined  crucible  and  covered  with  charcoal.  A 
lid  is  luted  on,  and  the  charge  is  then  very  strongly  heated  for 
one  hour.  This  assay  gives  a  good  yield. 

Modifications  become  necessary — 

1.  When  the  ore  contains  many  earthy  admixtures.     The  ore, 
before   it   is   reduced,   must   be   washed   in    a   vanning  trough, 
in  spitz-glasses  (Fig.  4,  p.  26),  or  in  a  beaker-glass  (as  silicic 
acid   especially   promotes    slagging   off  of  tin).      This   manip- 
ulation is  effectual  on  account  of  the  high  specific  gravity  of 
tin,  but  metallic  admixtures  cannot  (or  can  only  partly)  be  re- 
moved by  it. 

Specific  gravities :   tinstone,  6.8  to  7  ;  native  bismuth,  9.6  to 

9.8  ;  tungsten,  7.2    to  7.5 ;  arsenical   pyrites,  6   to  6.4 ;  copper 
glance,  5.5  to  5.8  ;  iron  pyrites,  4.9  to  5.1  ;  copper  pyrites,  4.1  to 
4.3 ;  molybdenite,  4.5   to  4.6 ;  magnetic   iron  ore,  4.8   to  5.2 ; 
specular  iron  ore,  6  to  6.5 ;  red  hematite,  4.5  to  4.6  ;  zinc  blende, 

3.9  to  4.2  ;  quartz,  2.65  to  2.80 ;  chlorite,  2.65  to  2.85  ;  slate,  2.5. 

2.  When  the  ore  contains  foreign  metallic  sulphides,  arsenides, 
and  antimonides. 

a.  The  unroasted  ore  is  either  digested  with  aqua  regia  for 
half  an  hour,  and  then  washed  by  decantation,  the  tungstic  acid, 
from  tungsten  ores,  if  any  be  present,  removed  by  digesting  with 
caustic  ammonia  for  half  an  hour  (the  flask  being  frequently 
shaken),  then  washed  by  decantation  and  dried  (Levoll\  and  then 
reduced : 

6.  Or,  the  dead-roasted  ore  is  treated  with  hydrochloric  acid 
as  long  as  the  acid,  after  the  ore  has  been  repeatedly  decanted 
and  washed,  appears  yellow,  when  a  fresh  addition  is  made  at  a 
boiling  temperature ;  the  ore  is  then  washed  by  decantation,  dried, 

»  Polyt.  Ctrbl.  1857,  p.  406. 
15 


226  ASSAYING. 

and  subjected  to  reducing  and  solvent  fusion  as  above  described 
(p.  224). 

3.  On  account  of  the  ease  with  which  tin  oxide  is  slagged  off. — 
For  these  reasons — 

a.  The  ore  is  intimately  rubbed  together  with  powdered  char- 
coal (p.  225),  or  carbonaceous  black-flux,  but  too  large  a  percent- 
age of  carbon  will  render  the  charge  more  refractory. 

b.  The  tin  oxide  is  reduced,  before  the  reducing  and  solvent 
fusion,  by  mixing  the  ore  with  |-  part  of  powdered  wood  char- 
coal and  igniting  it  in  the  crucible.     It  is  then  charged  as  above, 

4.  When  separate  grains  of  tin  are  found. — These  must  be 
collected    wTith    copper    (bronze    being    formed),    by    mixing    5 
grammes  of  ore  with   5  grammes  of  pure   copper  oxide  (with 
79.14  Cu).    The  mixture  is  placed  in  a  suitable  crucible  (Fig.  52, 
p.   65)  when    15   grammes   of  black   flux    and    1.25   grammes 
of  borax-glass  are  added,  together  with  a  cover  of  common  salt  and 
a  fragment  of  coal.    The  charge  is  gradually  heated  to  a  high  tem- 
perature, and  after  the  "  flaming"  has  ceased,  is  exposed  for  three- 
quarters  to  one  hour  to  a  white  heat  in  the  muffle  or  wind  furnace, 
or  for  one-half  to  three-quarters  of  an  hour  in  the  blast  furnace. 
It  is  then  taken  out,  and,  when  it  has  become  cold,  the  brittle 
bronze  button  is  freed  from  slag  and  weighed.     The  weight  of 
the  copper  contained  in  the  copper  oxide,  which  was  added,  is 
deducted.     If  the  copper  oxide  is  not  entirely  pure,  5  grammes 
of  it  are  fused  with  the  same  additions  as  given  above  and  the 
weight  of  the  resulting  copper  button  is  deducted  from  that  of 
the  bronze  button. 

5.  When  tin  oxide  is  combined  with  silicate  (as,  for  instance, 
in  tin-ore  slags),  5  to  25  grammes  of  slag  are  pulverized  as  finely 
as  possible,  the  metallic  tin  is  sifted  out  and  the  fine  substance  is 
gradually  added  to  12  to  15  times  the  quantity  of  potassium 
bisulphate,  which  has  been  previously  fused  in  an  iron  or  porce- 
lain crucible  under  the  muffle.     The  mixture  is  then  fused  until 
no  more  gas  bubbles  are  formed.     The  fused  mass  is  then  ex- 
tracted  with    boiling  water,  washed  with   hot   water,  and   the 
residue  reduced  as  above.     Or,  25  grammes  of  slag  are  mixed 
with  10  grammes  of  ferric  oxide,  6  grammes  of  fluor-spar,  and 
100  grammes  of  charcoal  powder.     The  mixture  is  placed  in  a 


TIN — FIRE   ASSAYS.  227 

covered  crucible  and  gradually  heated  to  a  strong  red  heat. 
This  is  kept  up  for  half  an  hour,  and  finally  kept  at  a  white  heat 
for  half  an  hour  longer. 

B.  Cornish  assay  of  tin. — 50  to  100  grammes  of  rich  tinstone 
are  mixed  with  one-fourth  the  quantity  of  anthracite  and  some 
fluor-spar.     A  large  wind  furnace,  such  as  is  used  for  assaying 
iron  (for  instance,  254  millimeters  wide,  178  millimeters  long, 
and  380  millimeters  deep),  is  filled  about  two-thirds  full  with 
coke,  and  brought  to  a  strong  red  heat.     A  few  pieces  of  fresh 
coke  are  then  added,  and  in  these  a  graphite  crucible  is  placed 
and  made  red  hot.     It  is  then  taken  out,  the  charge  poured  into 
it  by  means  of  an  open  mixing  scoop,  and  the  crucible  covered. 
The  charge  is  then  fused  for  20  minutes,  when  the  white-hot 
crucible  is  taken  out,  and  the  contents  are  poured  into  an  iron 
ingot  mould.    The  ingot  is  freed  from  slag.    The  slag  is  pounded 
fine  and  sifted  through  a  sieve  of  tin  plate  having  meshes  about 
as  large  as  a  pin-head.      The  tin  remaining  in  the  sieve  is  added 
to  the  ingot  of  tin,  while  the  fine  stuff  that  has  passed  through 
the  sieve  is  washed  and  floated  in  a  vanning  shovel  (Fig.  5,  p. 
27).     The  metallic  residue  from  the  Avashing  is  placed  in  a  dish 
and  dried.    The  three  lots  of  tin  are  then  weighed  together.    The 
ingot  of  tin  is  now  refined  by  smelting  it  in  an  iron  spoon.     The 
film  which  is  formed  during  this  operation  is  removed  until  the 
liquid  metal  has  a  bright  non-iridescent  surface.    It  is  then  poured 
into  a  gutter  in  a  marble  plate,  and  the  quality  of  the  tin  judged 
by  the  surface  and  ductility  of  the  resulting  rod  of  metal.    When 
lead  and  copper  are  present,  the  surface  will  exhibit  a  play  of 
colors  and  will  be  crystalline,  especially  towards  the  centre.  This 
assay  yields  about  10  per  cent,  less  than  the  true  percentage. 

The  Cornish  assay  is  less  accurate  than  the  German,  but  an 
experienced  assay er  obtains  results  which  compare  well  with  those 
obtained  on  a  large  scale,  and  it  allows  him  to  form  a  judgment 
of  the  quality  of  tin  which  an  ore  may  be  expected  to  yield,  and 
to  fix  the  price  to  be  paid  for  it  accordingly.1 

C.  LevoVs  assay  with  potassium  cyanide.2 — A  sufficient  quantity 

*  B.  u.  h.  Ztg.  1862,  p.  261. 

2  Journ.  fur  prakt.  Chemie,  xcv.  503. 


228  ASSAYING. 

of  powdered  potassium  cyanide  is  rammed  into  a  capacious  porce- 
lain or  fire-clay  crucible  to  form  a  layer  of  from  12  to  15  milli- 
meters thick,  5  grammes  of  the  powdered  ore,  intimately  mixed 
with  5  times  the  quantity  of  potassium  cyanide,  are  added  to  that 
in  the  crucible,  and  the  whole  covered  with  a  thin  layer  of  the 
cyanide.  The  charge  is  then  heated  in  a  moderate  fire  until  it 
fuses,  and  is  kept  in  constant  fusion  for  10  minutes.  The  crucible 
is  then  taken  out,  and  gently  tapped  to  facilitate  the  formation 
of  a  single  button,  and  allowed  to  cool.  The  button  is  then  freed 
from  adhering  slag  by  water.  In  case  copper  or  lead  is  present, 
the  ore  must  be  freed  from  them  before  the  reduction,  by  treating 
it  with  acid.  This  is  the  most  accurate  method  of  assaying  tin 
(to  within  one-half  per  cent.),  and  can  be  executed  in  a  very  short 
time.  In  case  the  ore  is  siliceous,  a  mixture  of  10  grammes  of 
ore,  3  to  8  grammes  of  ferric  oxide,  and  40  grammes  of  potassium 
cyanide,  is  placed  in  a  crucible  (Fig.  53,  p.  65)  lined  with  char- 
coal. The  mixture  is  first  covered  with  potassium  cyanide  and 
then  with  powdered  charcoal.  The  cover  is  luted  on  and  the 
charge  heated  at  a  high  temperature  for  one-half  to  one  hour. 

In  any  case  it  is  always  better  to  mix  a  small  quantity  of  pow- 
dered charcoal  with  the  charge.  One-half  of  the  potassium  cyanide 
may  be  mixed  with  the  ore  and  balance  used  to  cover  the  charge. 
Care  must  be  taken  not  to  allow  the  fire  to  become  too  hot  or  the 
charge  to  boil  over.  After  pouring,  the  mould  must  not  be  moved 
until  the  slag  has  set,  otherwise  it  is  apt  to  penetrate  into  the 
button. 

53.    WET   ASSAYS. 

A.   Gravimetric  assays. 

1.  1  gramme  of  tinstone  is  digested  with  diluted  aqua  regia  ; 
the  residue  is  washed  by  decantation  and  dried.  The  dry  mass 
is  then  fused  with  3  parts  sulphur  and  3  parts  sodium  carbonate. 
The  soluble  double  sulpho-salt  of  sodium  and  tin  is  lixiviated 
with  water,  and  the  tin  sulphide  precipitated  with  hydrochloric 
acid.  Sulphuretted  hydrogen  is  then  introduced  into  the  liquid, 
the  resulting  precipitate  is  filtered,  dried,  roasted,  and  finally 
weighed  as  stannic  acid,  containing  78  per  cent.  tin.  By  another 


TIN — WET   ASSAYS.  229 

method  the  ore  is  digested  in  aqua  regia  for  half  an  hour,  then 
washed  by  decantation  and  dried.  It  is  then  introduced  into  a 
silver  crucible  (standing  in  a  clay  crucible),  with  4  times  the 
quantity  of  caustic  potassa  dissolved  in  water,  the  very  finely 
powdered  tinstone  is  stirred  into  it,  and  the  whole  brought  to 
dryness.  It  is  then  fused  at  a  low  red  heat  for  half  an  hour. 
The  mass,  when  cold,  is  treated  with  diluted  hydrochloric  acid 
and  evaporated  to  dryness.  The  dry  mass  is  then  taken  up  in 
some  hydrochloric  acid,  gently  heated,  filtered,  and  precipitated 
with  sulphuretted  hydrogen.  The  sulphide  is  washed,  dried,  and 
roasted,  some  ammonium  carbonate  being  added  towards  the  end 
of  the  operation.  The  tin  oxide  is  then  weighed. 

2.  The  ore  is  digested  with  aqua  regia,  the  residue  with  some 
charcoal  is  placed  in  a  porcelain  crucible  and  heated  to  redness. 
The  reduced  tin  is  dissolved  in  hydrochloric  acid,  and  precipitated 
from  the  solution  with  zinc,  which,  in  the  form  of  a  flat  button 
fastened  on  the  end  of  a  copper  wire,  is  suspended  in  the  fluid. 
According  to  the  proportion  of  free  acid  present,  the  tin  will  ap- 
pear in  brilliant  needles,  in  scales,  mossy  or  spongy ;  the  latter 
condition  indicating  the  termination  of  precipitation.  The  zinc 
button  is  now  taken  from  the  liquor,  free  from  the  tin,  and  this 
is  pressed  together  in  an  agate  mortar.  It  is  then  dried  and 
fused  to  a  button  with  some  sterine  (Moissenet1).  Or,  the  ore  is 
digested  with  aqua  regia,  decomposed  with  potassium  hydrate, 
and  a  solution  of  stannic  chloride  in  hydrochloric  acid  is  formed 
as  above.  The  tin  is  precipitated  by  a  rod  of  zinc.  It  is  then 
washed  and  dried,  treated  with  strong  nitric  acid,  and  evaporated 
to  dryness.  When  cold,  it  is  moistened  with  diluted  nitric  acid 
and  filtered.  The  tin  oxide  is  then  dried,  ignited,  and  weighed. 
Lead  and  copper  are  removed  by  the  aqua  regia  at  the  commence- 
ment of  the  operation,  or  when  the  precipitated  tin  is  dissolved 
in  nitric  acid. 

Determination  of  tin  in  tin  slags. — The  following  method  is  re- 
commended by  Fresenius  and  Hintz.2  About  3  grammes  of  the 
finely  powdered  assay  material  are  treated  with  aqua  regia,  after 

1  B.  u.  h.  Ztg.  1861,  p.  170. 

2  Ztschft.  Anal.  Chern.,  XXIV.,  p.  412. 


230  ASSAYING. 

heating  the  solution  is  diluted  with  water  and  the  insoluble  residue 
filtered  off,  and  washed  with  water  containing  ammonium  nitrate. 
Make  filtrate  alkaline  with  caustic  soda  and  digest  for  a  considerable 
time  with  an  excess  of  sodium  sulphide.  The  resulting  precipitate  is 
filtered  off  and  repeatedly  treated  with  sodium  sulphide  in  the  same 
manner.  The  insoluble  residue  is  separated  from  filter  and  dried. 
The  latter  is  incinerated  at  a  low  temperature,  the  resulting  ash  added 
to  above  residue,  the  whole  fused  with  sulphur,  taken  up  with  water 
and  filtered.  The  filtrate  is  mixed  with  the  precipitate  obtained  with 
sodium  sulphide,  acidulated  with  HC1  and  the  precipitate  obtained 
treated  with  bromo-hydrochloric  acid.  It  is  then  filtered,  the 
filtrate  mixed  with  potassium  chloride,  and  evaporated  to  dry- 
ness.  In  case  tungstic  acid  separates,  the  filtering  must  be  re- 
peated. Precipitate  the  tin  in  the  filtrate  with  ammonium  nitrate. 
The  tungstic  acid  precipitated  by  the  treatment  with  bromo-hydro- 
chloric acid  as  well  as  that  separated  by  evaporation,  is  fused  with 
five  times  its  weight  of  potassium  cyanide,  whereby  any  tin  con- 
tained in  it  is  obtained  as  metal,  whilst  the  tungstic  acid'  passes 
into  the  flux.  The  precipitate  obtained  with  ammonium  nitrate  is 
fused  in  the  same  manner  with  KCy,  the  tin  being  obtained  in 
metallic  state.  The  insoluble  residue,  however,  is  repeatedly  fused 
with  KCy,  the  resulting  globules  of  tin  being  each  time  washed 
and  picked  out.  The  gray  powder  which  finally  remains,  as  well 
as  the  impure  tin  obtained  from  the  tungstic  acid,  is  fused  with 
sulphur,  taken  up  with  water,  filtered,  the  filtrate  acidulated  with 
H2S04,  and  the  precipitated  metallic  sulphides  dried.  They  are 
then  heated  in  a  porcelain  dish  in  a  current  of  hydrogen.  The  re- 
sulting residue  is  heated  in  air  and  fused  with  KCy.  The  tin 
thus  obtained  is  added  to  the  above,  dried  at  100°  -C.,  and 
weighed.  As  this  tin  is  not  entirely  pure  it  is  dissolved  in  HC1, 
the  impurities  partially  remain  undissolved  and  partially  escape  as 
hydrogen  combinations.  The  latter  are  caught  in  a  silver  solution 
and  determined  as  well  as  the  portion  remaining  undissolved.  The 
content  of  pure  tin  is  known  by  deducting  the  amount  of  the  im- 
purities thus  obtained. 

B.    Volumetric  assays. 

1.  Determination  of  tin  by  means  of  iodine. — A  few  drops  of 
potassium  iodide  of  any  desired  concentration  are  added  to  the 
acid  solution  of  stannous  chloride,  and  then  a  few  drops  of  diluted 


TIN — WET   ASSAYS.  231 

starch  paste.  A  solution  of  potassium  bichromate  of  0.02  or  0.01 
gramme  of  the  salt  in  1  cubic  centimeter  is  now  added  drop  by 
drop  under  constant  stirring,  until  the  separated  iodine  does  not 
again  disappear,  and  the  starch  assumes  a  blue  color  when  all 
the  stannous  chloride  has  been  converted  into  stannic  chloride 
(3SnO  4-  Cr2O6=  3SnO2  +  Cr2O3).  The  quantity  of  chromate  de- 
composed by  100  parts  of  pure  tin  dissolved  in  hydrochloric  acid 
is  empirically  determined  (100  tin  83.2  chromate). 

One  to  2  grammes  of  tinstone  are  placed  with  four  times  the 
quantity  of  potassium  cyanide  in  a  porcelain  dish,  and  heated  for 
fifteen  or  twenty  minutes.  The  mass  is  then  poured  upon  an 
iron  plate  and  treated  with  water.  The  metallic  residue  (tin  and 
iron)  is  dissolved  in  hydrochloric  acid,  the  tin  precipitated  with 
zinc,  again  (dissolved  in  hydrochloric  acid,  and  titrated  with 
potassium  bichromate  in  the  presence  of  potassium  iodide  and 
starch.  (Hart.)1 

According  to  Lenssen*  more  accurate  results  may  be  obtained 
by  dissolving  stannous  salts  (stannous  chloride)  with  an  addition 
of  tartaric  acid,  or  potassium-sodium  tartrate,  in  sodium  bicarbo- 
nate. Some  starch  paste  is  added  to  the  clear  solution,  and  it  is 
then  titrated  with  solution  of  iodine  until  the  blue  color  appears 
(SnO  +  214-  Na,O = SnO2  +  2NaI).  The  iodine  solution  is  stan- 
darized  by  dissolving  12.7  grammes  of  pure  iodine,  and  20  to  30 
grammes  of  potassium  iodide  in  1000  cubic  centimeters  of  dis- 
tilled water.  A  quantity  of  pure  tin,  accurately  weighed,  is  dis- 
solved in  hydrochloric  acid,  tartaric  acid  is  added,  and  the  solution 
supersaturated  with  sodium  bicarbonate.  Solution  of  starch  is 
added,  and  the  iodine  solution  is  gradually  added  from  the  burette 
until  the  liquid  becomes  blue.  Two  atoms  of  iodine  (254)  cor- 
respond to  one  atom  of  tin  (118).  This  assay  may  be  especially 
recommended  for  the  detection  of  small  quantities  of  tin. 

2.  Determination  of  tin  by  means  of  potassium  permanganate. — 
5  to  10  cubic  centimeters  of  solution  of  stannous  chloride  are 
treated  with  a  boiling  solution  of  ferric  chloride  containing  free 
hydrochloric  acid  (Snd2  +  Fe2Cl6= SnCl4  4-  2FeCl3).  The  ferrous 

1  Dingier,  ccx.  394. 

2  Jouru.  f.  prakt.  Chem.  Ixxviii.  200.     Mohr,  Titrirmethode,  1874,  p.  311. 


232  ASSAYING. 

chloride  which  is  formed  is  titrated,  after  dilution  with  water, 
with  standard  solution  of  potassium  permanganate,  until  the 
liquid  becomes  reddish  (p.  123).  The  value  of  the  standard 
solution  is  determined  by  placing  0.2  gramme  of  freshly  pre- 
cipitated tin  in  a  platinum  crucible,  and  dissolving  it  in  hydro- 
chloric acid,  in  a  current  of  carbonic  acid.  Ferric  chloride  in 
excess  is  added,  and  then  the  solution  of  potassium  permanganate  is 
added,  until  the  last  drop  colors  the  fluid  perceptibly.  2  equiva- 
lents of  iron  =>  1  equivalent  of  tin.  A  correction  becomes  neces- 
sary, as  experience  has  shown  that  more  potassium  permanganate 
is  consumed  in  titrating  ferrous  chloride  than  stannous  chloride. 

3.  Determination  of  lead  in  tin.1 — According  to  Roux,  the  fol- 
lowing method  is  used  in  the  Paris  Municipal  Laboratory:  2.5 
grammes  of  the  metal  are  treated  in  a  ^  liter  flask  with  15  c.c.  of 
HN03,  and  the  nitrous  vapors  expelled  by  boiling ;  40  c.c.  of  a  satu- 
rated solution  of  sodium  acetate  are  added,  and  the  flask  filled  up 
to  mark.  When  the  precipitate  has  settled  100  c.c.  of  the  clear 
supernatant  liquid  are  taken  out,  10  c.c.  of  a  solution  of  potassium 
bichromate  (7.13  grammes  to  the  liter)  are  then  added,  and  the  lead 
chromate  allowed  to  settle,  another  10  c.c.  of  the  potassium  bichro- 
mate are  added,  and  the  same  operation  repeated  until  the  superna- 
tant liquid  indicates  an  excess  of  lead  chromate.  Filter  the  pre- 
cipitate, and  determine  the  excess  of  lead  chromate  by  a  solution  of 
t5  grammes  of  ammonium-ferric  sulphate  and  25  grammes  of 
H2S04  to  the  liter. 

Detection  of  tin  in  presence  of  antimony. — According  to  Muir,2 
it  is  detected  in  the  HC1  solution  by  boiling  with  copper  turnings 
for  about  ten  minutes.  This  is  reduced  to  stannous  form  and 
permits  of  being  detected  with  mercuric  chloride  (HgCl2). 

C.  Electrolytic  determination  of  tin. — Tin  can  be  very  easily  de- 
termined by  this  means  ;  it  separates  completely  from  a  HC1  solu- 
tion containing  a  little  free  acid,  from  the  ammonium  double  ox- 
alate,  or  from  ammonium  sulphide  solution.  Sodium  and  potassium 
sulphides  cannot  be  used,  as  tin  separates  only  partially  from  a 
dilute  solution  of  such  salts,  and  not  at  all  from  a  concentrated  solu- 
tion. Potassium  oxalate  cannot  be  used ;  since,  in  this  case,  a  basic 

1  Bull.  Soc.  Chim.,  XXXV.,  p.  596.     Chemikerztg,  1881,  441. 

2  Chem.  News,  xlv.  p.  69. 


BISMUTH ORES.  233 

salt  separates  at  the  positive  pole  and  cannot  be  reduced.  If  an 
acid  solution  is  used,  the  current  must  not  be  interrupted  during 
the  washing ;  this  precaution  is  unnecessary  when  ammonium  ox- 
alate  or  sulphide  is  used.  When  a  solution  of  the  double  oxalate 
is  used,  it  is  freed  as  fully  as  possible  from  acid,  treated  with  am- 
monium oxalate  solution,  then  heated,  and  3  or  4  grammes  more  of 
ammonium  oxalate  added.  The  hot  solution  is  treated  with  a  cur- 
rent of  9  to  10  c.c.  oxy hydrogen  gas  per  minute.  The  precipitation 
is  complete  in  about  five  hours;  the  solution  is  then  poured  off,  and 
the  metal  treated  as  usual.  In  the  solution  of  the  ammonium 
sulpho-salt,  tin  behaves  like  antimony.  The  tin  solution  (neutral- 
ized if  necessary  with  ammonia)  is  treated  with  just  sufficient  am- 
monium sulphide  to  form  the  sulpho-salt,  diluted  to  200  c.c.,  and 
electrolyzed.  The  precipitation  is  complete  in  5  or  6  hours.  Should 
any  sulphur  adhere  so  strongly  to  the  tin  that  it  cannot  be  washed 
off,  it  can  easily  be  removed,  after  washing  with  alcohol,  by  gentle 
rubbing  with  a  linen  cloth.  In  gravimetric  analysis  tin  is  often 
separated  from  other  metals  by  sodium  sulphide  instead  of  am- 
monium sulphide.  To  determine  tin  electrolytically  in  such  cases, 
the  sodium  sulphide  must  be  converted  into  ammonium  sulphide. 
To  accomplish  this,  the  solution  is  treated  with  about  25  grammes 
of  pure  ammonium  sulphate  free  from  iron,  and  heated  very  care- 
fully, with  the  dish  covered,  till  the  H2S  has  all  escaped ;  the  solu- 
tion is  then  kept  in  gentle  ebullition  for  about  fifteen  minutes. 
After  it  is  completely  cool,  any  sodium  sulphate  that  may  have 
separated  is  dissolved  by  the  addition  of  water,  and  the  solution 
electrolyzed  with  a  current  of  9  to  10  c.c.  of  oxyhydrogen  gas  per 
minute.1 

XL  BISMUTH, 

54.   ORES. 

Native  bismuth,  bismuth  glace,  Bi2S3,  with  81.25  Bi ;  cupriferous 
bimiuth,  CuBiS2,  with  62  Bi  and  18.9  Cu  ;  tetradymite,  Bi2Te3,  with 
51.94  Bi;  bifmuth  ochre,  Bi2O3,  with  89.65  Bi,  and  others. 

1  Quant.   Chem.  Anal,  by  Electrolysis.     Classen.     [Trans.]     New  York. 

1887. 


234  ASSAYING. 

55.    FIRE   ASSAYS. 

These  are  inaccurate,  as  bismuth  volatilizes,  and  in  case  the  ore 
is  impure,  foreign  metals  collect  in  the  brittle  button. 

1.  Ores   and  compounds  free  from   sulphur  (native   bismuth, 
tetradymite,  bismuthic  cupel  ash,  etc.).     5  grammes  of  ore  with 
two  and  a  half  to  three  times  the  quantity  of  black  flux,  or  potash 
and  flour,  and  2.5  to  5  grammes  of  borax-glass,  are  placed  in  a 
suitable  crucible  (Fig.  52,  p?  65)  and  covered  with  a  layer  of 
common   salt.     It   is   then   placed   in   a   muffle,  and,  after  the 
"flaming"  has  ceased,  fused  for  twenty-five  to- thirty  minutes  at 
not  too  high  a  temperature.    Or,  10  to  20  grammes  of  the  substance 
are  heated  with  two  and  a  half  to  three  times  the  quantity  of 
borax-glass,  an  equal  weight  of  soda,  and  5  to  10  grammes  of 
potassium  cyanide,  with  a  covering  of  common  salt.     Lead,  tin, 
and  copper  pass  partly  into  bismuth,  and  must  be  removed  by  the 
wet  method.1 

2.  Sulphurized  bismuth  ores. — Five  grammes  of  ore  are  placed 
in  a  crucible  and  covered  with  1.25  to  1.5  grammes  of  thick  iron 
wire,  and  2.5  to  10  grammes  of  fine  shreds  of  silver  ;  upon  this 
are  placed  two  and  a  half  to  three  times  the  quantity  of  black  flux 
or  potassium  carbonate  and  flour,  on  this  1J  to  2  grammes  of 
borax,  and  a  covering  of  salt.     The  charge  is  fused  as  in  the  lead 
assay,  when  the  sufficiently  ductile  alloy  of  silver  with  bismuth 
can  be  separated  from  the  iron.     The  percentage  of  bismuth  is 
found  by  deducting  the  silver  added.     Arsenic  must  be  removed 
by  a  previous  ignition  of  the  ore,  with  exclusion  of  air;   but 
antimony,  with  an  admittance  of  air.     Lead  passes  into  the  bis- 
muth, and  copper,  if  not  too  much  of  it  is  present,  is  slagged  oif. 

Joachimsthal :  5  grammes  of  ore  are  fused  with  2  grammes  of 
sodium  carbonate  and  1.25  grammes  of  iron  turnings  with  a  cov- 
ering of  common  salt.  The  resulting  plumbiferous  button  is  dis- 
solved in  nitric  acid,  the  lead  is  separated  as  lead  chloride  by 
Patera's  method,  which  will  be  given  later  on,  or  the  bismuth 
separated,  as  metal,  from  a  weak  acid  solution  by  means  of  a 
strip  of  lead.  Tamm's  process :  Ore  free  from  copper  is  fused 
with  a  flux  consisting  of  2  parts  potassium  or  sodium  carbonate,  and 


BISMUTH — WET   ASSAYS.  235 

1  part  common  salt,  with  an  addition  of  some  potassium  cyanide. 
Cupriferous  ores:  3  parts  of  ore  with  5  parts  potassium  or  sodium 
carbonate,  2  parts  common  salt,  1  part  powdered  wood-charcoal, 
and  2  parts  flowers  of  sulphur.  The  bismuth  is  separated  (with 
about  8  per  cent,  loss),  containing  a  little  copper,  most  of  the  lat- 
ter passing  into  the  slag  as  sulphide.  The  presence  of  iron  in- 
duces more  copper  to  unite  with  bismuth ;  antimony  and  arsenic 
and  lead  (partly)  pass  into  the  slag.  Rose  fuses  the  ore  with  5 
times  the  quantity  of  potassium  cyanide,  in  a  porcelain  crucible, 
washes  the  resulting  metal  grains  quickly  with  water,  then  with 
dilute  alcohol,  and  weighs.  In  fusing,  no  black  pulverulent  resi- 
due of  bismuth  sulphide  must  remain. 

56.    WET   ASSAYS. 

While  the  volumetric  assays1  which  have  been  recommended  are 
of  no  practical  importance,  the  gravimetric  methods  are  mostly 
complicated,  the  available  docimastic  tests  being,  as  a  general 
rule,  limited  to  the  separation  of  bismuth  from  lead. 

A.  Assay  of  ore. — 2  to  3  grammes  of  ore  are  dissolved  in  nitric 
acid,  and  evaporated  to  dryness.     Some  sulphuric  acid  is  then 
added,  the  mass  stirred,  and  again  evaporated  to  dryness.     The 
residue    is   now  dissolved   in  water,  and  filtered.     The  filtrate 
is  precipitated  with  ammonium  carbonate  in  excess,  filtered  oiF, 
washed,  dried,  ignited,  and  then  weighed  as  oxide,  containing 
89.65  per  cent,  bismuth. 

B.  Separation  of  bismuth  from  lead. 

1.  According  to  Patera. — The  plumbiferous  bismuth  is  dis- 
solved in  nitric  acid.  The  solution  is  considerably  diluted  with 
water,  upon  which  the  liquid  must  not  become  turbid.  The  bis- 
muth is  then  precipitated  from  the  weak  acid  solution  with  a 
bright  strip  of  lead.  The  pulverulent  black  bismuth  is  removed, 
and  washed  with  water  and  alcohol.  It  is  then  dried  at  a  tem- 
perature not  over  120°  C.  (248°  F.),  and  weighed.  Or,  hydro- 
chloric acid  in  excess  is  added  to  the  diluted  nitric  acid  solution, 

J  Fleischer,  Titrirmethode,  1876,  p.  87.  Muir.  in  Ber.  d.  deutsch.  chem. 
Gesel.  1877,  p.  2051.  Buisson,  in  Fresenius's  Ztschr.  1874,  p.  61.  Pearson, 
in  Mitchell's  Practical  Assaying,  1888,  p.  817. 


236  ASSAYING. 

* 

and  then  some  strong  alcohol ;  the  silver  chloride  and  lead  chlo- 
ride are  filtered  off,  and  the  bismuth  is  precipitated  from  the 
filtrate  with  ammonium  carbonate.  The  carbonate  is  washed, 
dried,  and  ignited,  and  the  bismuth  determined  as  oxide  (Bi2O3 
with  -89.65  Bi). 

Determination  of  the  percentage  of  lead  and  silver. — The  com- 
bined metallic  chlorides  are  weighed  upon  a  weighed  filter  and 
then  cupelled.  The  silver  is  calculated  to  silver  chloride,  the 
yield  deducted  from  the  weight  of  the  combined  chlorides,  and 
the  lead  calculated  from  the  lead  chloride  found  by  difference. 
Copper  is  determined  by  evaporating  the  ammoniacal  filtrate  to 
dryness  with  sulphuric  acid.  The  dry  mass  is  taken  up  in  water, 
and  the  copper  precipitated  with  iron  or  zinc  (p.  106). 

2.  According  to  Ullgreen. — The  solution  of  bismuth  in  nitric 
acid  is  precipitated  with  ammonium  carbonate.  The  lead  and 
bismuth  carbonates  are  dissolved  in  acetic  acid,  and  the  bismuth 
is  precipitated  in  a  well-closed  vessel  with  a  bright  strip  of  lead. 
It  is  then  filtered,  washed,  and  dissolved  in  nitric  acid.  The 
mass  is  then  evaporated  to  dryness  and  heated,  when  bismuth 
oxide  remains  behind. 

Tin  oxide  (also  antimonious  acid)  remains  behind  in  nitric  acid 
in  dissolving  the  alloy.  The  residue  is  then  washed  with  alcohol, 
dried  and  weighed.  Lead  and  bismuth  are  precipitated  from  the 
filtrate  with  ammonium  carbonate  (see  above),  and  the  copper 
from  the  filtrate  as  above. 

Electrolytic  assay. — Smith  and  Knerr1  find  that  bismuth  can  be 
completely  and  rapidly  precipitated  by  electrolysis  from  a  sulphate 
solution  containing  free  H2S04.  They  add  1  c.c.  of  H2SO4  to  25  c.c. 
of  solution,  and  use  a  current  of  1  to  4  c.c.  of  oxyhydrogen  gas  per 
minute. 

XII,  MERCURY, 

57.    ORES. 

Cinnabar,  HgS,  with  86.2  Hg;  native  mercury,  mercurial 
tetrahedrites,  with  0.5  to  17  per  cent.  Hg. 

i  Am.  Chera.  Journ.,  VIII.,  p.  207. 


>^vv 

f  OF  THE 

B    UNIVERSITY 
V         OF 

^sg^FOF...., 
MERCURY — FIRE   ASSAYS.  ""237 


58.    FIRE   ASSAYS. 

The  object  of  these  assays  is  to  separate  the  sulphur,  either  by 
union  with  alkalies,  iron,  lime,  etc.,  or  to  oxidize  it  by  means  of 
lead  oxide,  by  heating  the  ores  in  retorts,  tubes,  or  crucibles,  and 
condensing  the  mercurial  vapors  liberated  into  liquid  mercury, 
which  is  weighed  either  by  itself,  or,  what  is  more  accurate,  in 
combination  with  gold.  In  smelting  works,  where  many  assays 
have  to  be  made,  small  distilling  furnaces1  are  generally  on 
hand  for  this  purpose.  Notwithstanding  the  defects  of  the  fire 
assays,  it  has  not  been  possible  to  replace  them  by  simple  wet 
methods.2 

A.  Assays  yielding  free  mercury. — 140  to  1800  grammes,- ac- 
cording to  richness,  of  cinnabar  ore,  are  heated  with  one  half  or 
equal  parts  of  black  flux,  or  50  per  cent,  iron  filings,  or  30  per 
cent,  lime,  and  30  per  cent.  powrdered  wood  charcoal,  either  in 
clay  or  iron  retorts,  in  the  latter  case  without  iron  filings  (native 
mercury  ore,  amalgam,  etc.,  it  is  best  to  heat  in  glass  retorts),  at 
a  slowly  increasing  heat,  in  a  suitable  furnace  (Figs.  44  to  46,  pp. 
61,62).  The  vapors  are  condensed  in  the  receivers  represented 
by  Figs.  44  to  46,  or  in  a  wet  linen  bag  tied  to  the  end  of  the 
stem  of  the  retort,  the  lower  part  of  the  stem  being  at  the  same 
time  kept  cool  by  moist  strips  of  linen  or  paper  tied  around  it. 
The  mercury  adhering  to  the  neck  is  removed  by  gently  tapping 
and  wiping  out,  and  that  from  the  receiver  is  dried  with  absorbent 
paper  and  caustic  lime,  and  weighed  in  a  watch-glass. 

Idria:3  140  grammes  of  ore,  with  two  or  three  spoonfuls  of 
powdered  lime,  are  placed  in  iron  distilling  tubes  of  about  52 
millimeters  diameter,  lying  in  two  rows,  one  above  the  other,  on 
each  side  of  a  furnance.  The  receivers  are  luted  on,  and  the 
process  is  finished  when  the  tubes  show  a  bright-red  heat.  The 
loss  of  mercury  is  considerable.4  Hungarian  mercurial  tetra- 
hedrite:5  The  ores  are  heated  with  the  same  quantity  of  iron 

1  B.  u.  h.  Ztg.  1854,  p.  394  (Idra). 

2  Muspratt's  Chem.  v.  1296.     Mohr,  Titrirmethode,  1874,  pp.  236,  318,  441, 
438. 

a  B.  u.  h.  Ztg.  1854,  p.  394.  4  B.  u.  h.  Ztg.  1854,  357. 

3  B.  u.  h.  Ztg.  1866,  pp.  24,  262. 


238 


ASSAYING. 


turnings — roasted  ore  at  the  same  time  with  an  equal  quantity  of 
lead  oxide1 — in  glass  retorts  resting  upon  clay  dishes.  The  neck 
of  the  retorts,  when  the  operation  is  finished,  are  broken  off  by  a 
blow,  and  the  mercury  is  removed  by  means  of  a  wiper  of  rabbit 
fur.  It  is  then  collected  into  a  globule  and  weighed.  Rose's 
niethod  :  A  body  of  magnesite  (or  chalk  with  an  equal  quantity 
of  sodium  bicarbonate),  26  to  52  millimeters  long  is  introduced 
into  a  glass  tube,  closed  at  one  end,  and  measuring  314  to  470 
millimeters  in  length,  and  9  to  13  millimeters  in  width.  Upon 
this  is  placed  an  intimate  mixture  of  the  ore  and  quicklime  in 
excess,  upon  this  more  lime  with  which  the  mortar  has  been 
cleaned  off,  then  more  quicklime,  and  upon  all  a  loose  plug  of 
asbestos.  The  open  end  of  the  glass  tube  is  drawn  out  and  bent 
to  ah  obtuse  angle,  and  introduced  into  a  narrow-necked  flask,  so 
that  its  end  just  touches  the  water  contained  therein.  The  hori- 
zontal part  of  the  tube  is  gradually  heated  from  front  to  back  in 
a  combustion  furnace,  such  as  is  used  for  organic  analysis  (Fig.  77, 

Fig.  77. 


without  the  cylinder  on  the  right).  When  the  operation  is 
finished,  the  bent  end  of  the  tube,  in  which  the  mercurial  vapors 
have  been  condensed,  is  cut  off,  and  the  mercury,  which  has  been 
protected  from  oxidation  by  the  current  of  carbonic  acid  which  is 
developed,  is  collected  in  the  matrass.  This  is  well  shaken  and 

1  Bergwerksfreund,  v.  127  (Berthier).    B.  u.  h.  Ztg.  1879,  p.  206*(Atwood). 


MERCURY — FIRE   ASSAYS.  239 

allowed  to  settle.  The  clear  water  is  then  poured  off,  and  the 
mercury  placed  in  a  previously  weighed  porcelain  crucible.  The 
water  still  adhering  to  it  is  removed  with  blotting  paper.  It  is 
then  dried  under  a  bell-glass  over  sulphuric  acid,  or  in  an  air-bath 
at  100°  C.  (212°  F.),  and  weighed. 

B.  Assays  in  which  the  mercury  is  determined  in  combination 
with  gold. — These  are  the  most  accurate  assays. 

1.  Eschka's  process.1 — The  quantity  of  ore  taken  for  the  assay 
varies  according  to  its  richness.  If  the  ore  carries  as  much  as  1 
per  cent.  10  grammes,  1  to  10  per  cent.  5  grammes,  and  over  10 
per  cent.  2  grammes  are  used.  The  sample  is  placed  in  a  porcelain 
crucible,  the  edge  of  which  has  been  ground  smooth,  and  mixed 
with  half  its  quantity  of  iron  filings  free  from  grease,  covered  writh 
a  layer  of  iron  filings  5  to  10  millimeters  thick.  A  well-fitting 
concave  cover,  made  of  fine  gold,  and  previously  accurately 
weighed,  and  the  concavity  of  which  is  filled  with  distilled  water, 
is  now  placed  on  the  crucible.  The  lower  part  of  the  crucible,  is 
heated  by  a  flame  for  about  10  minutes,  during  which  time  the 
mercury  is  volatilized,  and  deposits  itself  on  the  gold.  The  gold 
cover  is  now  removed,  the  water  in  its  concavity  poured  off, 
and  the  mirror  of  mercury  washed  with  alcohol.  The  cover  is 
then  dried  for  about  two  or  three  minutes  in  the  water-bath, 
placed  upon  a  tared  porcelain  crucible  and  allowed  to  cool  in  the 
desiccator,  and  then  both  the  mercury  and  crucible  are  weighed 
together.  The  most  accurate  results  are  obtained  in  the  case  of 
poor  ores  carrying  up  to  10  per  cent.  Hg. 

The  crucible  should  be  heated  very  gradually,  and  the  tempera- 
ture only  slightly  raised  towards  the  end  of  the  operation.  The 
water  evaporated  from  the  gold  lid  during  the  assay  must  be  con- 
stantly replaced,  and  the  lid,  after  the  assay  is  finished,  dried  in  an 
air-bath.  The  distillation  of  the  mercury  out  of  the  lid  must  at  first 
be  done  at  a  very  moderate  heat,  and  the  temperature  only  raised 
when  the  mercury-mirror  has  disappeared,  otherwise  the  gold  is 
apt  to  volatilize  with  the  mercury,  and  the  lid  to  become  spongy. 
If  the  assay  material  contains  so  much  mercury  that  it  is  deposited 

1  Oestr.  Ztschr.  f.  Berg.  n.  Htittenwes,  1872,  No.  9.  B.  u.  h.  Ztg.  1872,  p. 
173. 


240 


ASSAYING. 


in  drops,  the  quantity  taken  must  be  reduced.  If  the  gold  lid,  after 
the  distillation  of  the  mercury,  shows  a  decrease  in  weight  as  com- 
pared with  that  previously  found,  it  is  probably  due  to  the  volatili- 
zation of  the  gold. 

In  Idria  (Austria)  this  assay  is  used  as  the  prevailing  working 
assay.  The  following  compensative  differences  are  allowed  in  the 
results : — * 

Amount  of  mercury  in  the  ore. 

0  to  0.4  per  cent. 

0.4  to    0.7  per  cent.  .        '.         . 

0.7  "    1.0       "  ...  .' 

1.0  "    3.0       "  .         '. 

3.0  "    5.0       "  .      •  ',.,  -   . 

5.0  "  10.0       "  .         »"."    . 

10.0  "  20.0       "  .         .    '    :. 

20.0  "  30.0       "  V-'      . 
30.0  "  maximum 


0.50 


Fig.  78. 


In  testing  for  less  than  0.001  gramme  of  mercury  Teuber'2  recom- 
mends the  following  method :    The  dry  and  finely  pulverized  assay 

material  is  mixed  in  a  porcelain  cru- 
cible, shown  in  Fig.  78  (|  actual  size), 
with  thoroughly  dried  iron  filings 
and  minium.  The  charge  is  covered 
with  a  layer  of  minium,  the  lid  luted 
on,  and  the  crucible  gradually  and 
carefully  heated  over  a  lamp.  The 
temperature  is  thus  slowly  raised  un- 
til the  bottom  of  the  crucible  shows  a 
scarcely  perceptible  glow.  The  drops 
of  moisture  which  condense  on  lid- 
tube  are  absorbed  with  blotting  paper. 
The  gold  dish  is  then  placed  upon  the 
tube  a,  b  (which  is  about  1  millime- 
ter in  diameter),  and  filled  with  water.  The  mercury  is  deposited 
as  a  metallic  mirror  on  the  spot  where  the  gold  dish  rests  upon  the 
tube.  If  the  deposit  of  mercury  is  not  too  thin,  its  presence  can  be 
confirmed  by  moistening  it  with  HN03,  drying,  and  testing  the 
nitrate  of  mercury  found  with  a  strip  of  filter  paper  moistened  with 

1  Fortschritte  im  Probirwesen,  Balling.     Berlin,  1887,  p.  142. 

2  Oesterr.  Ztschft.  f.  Bg.  u.  Httuwsn,  1879,  p.  423. 


MERCURY — WET   ASSAYS.  241 

potassium  iodide ;   the  characteristic   red  color  of  mercuric  iodide 
will  immediately  appear. 

2.  Kustel's  assay.1 — This  is  executed  in  a  manner  similar  to  the 
above,  before  the  blowpipe,  with  the  difference  that  the  heating  is 
done  in  a  tube,  the  front  end  of  which  is  provided  with  a  gold 
spiral. 

C.  Assay  of  cinnabar. — 10  grammes  of  cinnabar  ore  are  intro- 
duced into  a  glass  retort  (Fig.  45,  p.  62),  and  heated.  The  sub- 
limate of  mercury  sulphide  which  deposits  itself  in  the  neck  of 
the  retort  is  collected  and  weighed.  Some  metallic  mercury  freed 
by, organic  substances,  which  may  have  been  present,  may  be 
mixed  with  the  sublimate.  This  is  removed  from  the  sublimate 
by  nitric  acid,  and  the  quantity  of  mercury  dissolved  ascertained 
by  the  difference  in  weight.  86  parts  of  mercury  correspond  to 
100  parts  of  cinnabar. 

59.    WET  ASSAYS. 

These  may  be — 

A.  Gravimetric  assay. — 1  gramme  of  cinnabar  is  heated  with 
aqua  regia,  and  repeatedly  evaporated  with  hydrochloric  acid,  in 
order  to  expel  the  nitric  acid.     The  solution  of  chloride  is  boiled 
with  stannous  chloride  in  excess,  the  clear  fluid  is  poured  off,  and 
the  beads  of  metal  are  collected   into  a  coherent  globule,  by 
heating  it  again  with  some  stannous  chloride  and  a  few  drops  of 
hydrochloric  acid.     The  mercury  is  then  washed  by  decantation, 
first  with  water  containing  hydrochloric  acid,  and  then  with  pure 
water.     It  is  now  introduced  into  a  small  porcelain  crucible, 
previously  weighed,  and  the  greater  part  of  the  adhering  water 
removed   by  means  of  filtering  paper.     The  mercury  is   then 
dried  in  a  desiccator  (Fig.  19,  p.  40),  with  concentrated  sulphu- 
ric acid,  and  weighed. 

B.  Volumetric  assays.2 — These   are  mostly  complicated,  and 
possess  no  advantage  over  the  ordinary  analytical  determination 

1  B.  u.  h.  Ztg.  1874,  p.  70. 

2  Mohr,  Titrirmethode,  1874,  pp.  236,  338,  436,  438,   441.      Fresenius's 
Ztschr.  ii.  381. 

16 


242  ASSAYING. 

by  weight,  or,  are  not  generally  available,  as  they  require  the 
absence  of  certain  metals. 

C.  Electrolytic  determination  of  mercury. — According  to  Es- 
cosura,1  0.5  gramme  of  the  ore  is  digested  with  10  to  15  c.c.  of  HC1 
and  20  c.c.  of  water  in  a  porcelain  dish ;  after  boiling  add  from  0.5 
to  1.0  gramme  of  potassium  chlorate  in  small  portions;  when  de- 
composition has  taken  place  dilute  with  50  c.c.  of  water  and  expel 
free  chlorine  by  continued  boiling.  In  order  to  separate  selenium 
or  tellurium,  if  present,  add  20  to  30  c.c.  of  a  saturated  solution  of 
ammonium  sulphate  and  boil  slightly ;  when  the  insoluble  residue 
has  settled,  filter,  and  use  filtrate  as  the  electrolytic  bath.  The  neg- 
ative electrode  should  be  a  pure  gold  and  the  positive  a  platinum 
sheet.  The  solution  is  subjected  to  the  galvanic  current  from  24  to 
30  hours.  The  increased  weight  of  the  gold  equals  the  content  of 
mercury.  Two  Bunsen  cells  are  generally  sufficient.  This  assay  may 
also  be  performed  by  treating  the  finely  pulverized  ore  in  a  platinum 
dish  with  HC1,  ammonium  sulphate,  and  water.  Of  10  per  cent,  ore 
only  0.2  gramme  is  used,  and  in  0.1  per  cent,  ore  10  grammes.  The 
platinum  dish  serves  as  the  negative  pole  and  a  disk  of  sheet  gold, 
about  4  centimeters  in  diameter,  as  the  positive  pole.  The  current 
is  supplied  by  6  Meidinger  cells,  and  the  mercury  is  precipitated  in 
24  hours. 

These  determinations  are  said  to  be  very  accurate  and  exclusively 
used  at  Almaden. 

According  to  Classen,2  mercury  is  precipitated  from  a  solution  of  its 
salt  acidified  with  HN03  by  a  current  of  0.2  to  0.5  c.c.  oxyhydrogen 
gas,  in  the  form  of  a  mirror  or  of  small  globules,  on  the  negative  elec- 
trode ;  the  metal  adheres  well  and  can  be  washed  without  loss.  The 
washing  must,  however,  be  done  without  interrupting  the  current. 
Insoluble  mercury  compounds  may  easily  be  analyzed  by  suspend- 
ing them  in  acidulated  water,  or  in  a  dilute  solution  of  comrnon  salt 
(1  :  10),  and  electrolyzing  as  usual. 

Smith  and  Knerr3  use  a  current  of  4  c.c.  oxyhydrogen  gas  per 
minute,  and  find  precipitation  complete  in  30  to  45  minutes,  the 
mercury  forming  a  compact  shining  deposit. 

1  Journ.  Pharm.  Chem.     1886.     p.  411.     Cliemikerztg.     1886.     p.  100. 

2  Quan.  Chem.  Analysis,  by  Electrolysis.     [Trans.]     New  York,  1887. 

3  Am.  Chem.  Journ.,  8,  p.  209. 


ANTIMONY — FIRE   ASSAYS.  243 

XIII.  ANTIMONY. 

60.   ORES. 

Stibnite  (antimony  sulphide),  Sb2S3,  with  71.77  Sb ;  valentinite 
(antimony  oxide),  Sb2O3,  with  83.56  Sb ;  pyrostilbite  (antimony 
oxymlphide),  Sb2O3.Sb2S3,  with  77.21  Sb. 

61.    FIRE  ASSAYS. 

The  assays  of  antimony  sulphide,  which  is  the  principal  ore, 
are  inaccurate  on  account  of  the  volatilization  of  antimony,  in- 
complete decomposition  by  alkaline  carbonates  and  even  by  potas- 
sium cyanide  (4  parts),  as  well  as  on  account  of  iron,  which 
always  passes  partly  into  the  antimony.  There  are  likewise  no 
simple  docimastic  tests  by  the  wet  method.1  Sometimes  the  yield 
of  antimony  sulphide  (antimoniun  crudum)  contained  in  the  ore 
is  ascertained  by  a  liquation  process  assay  on  a  small  scale. 

A.  Liquation  process  for  determining  antimonium  crudum. — 1 
to  1 J  kilogrammes  of  ore  comminuted  to  fragments  the  size  of  a 
hazel-nut  or  walnut  are  introduced  into  a  covered  crucible  having 
a  perforated  bottom  and  fitting  air-tight  in  another  crucible  in 
such  a  manner  that  sufficient  space  is  left  between  the  two  to 
allow  the  fused  antimony  sulphide  to  collect  in  the  lower  crucible. 
The  lid  and  the  joint  between  the  two  crucibles  should  be  luted 
with  fire-clay  and  sand.  The  lower  crucible  is  surrounded  with 
some  poor  conductor  of  heat  (ashes),  and  the  upper  ore  with  live 
coals,  kept  in  a  glow  with  a  bellows,  and  heated  to  a  moderate 
red  heat.  The  antimony  sulphide  will  melt  and  collect  in  the 
lower  crucible. 

jB.  Determination  of  antimony  in  antimony  sulphide. 

1.  Assay  by  precipitation. — 5  grammes  of  ore  are  fused  in  a 
crucible  with  the  same  or  double  the  quantity  of  black  flux,  or 

1  Fresenius's  Ztsch.  xvii.  185  (Becker's  gewichtsanalytische  Probe)  ;  Mohr, 
Titrirmethode,  1874,  p.  267,  309  ;  Muspratt's  Chemie,  i.  820;  Fleischer,  Titrir- 
methode,  1876,  p.  299. 


244  ASSAYING. 

potassium  carbonate  and  flour,  about  2  grammes  of  iron  filings, 
0.75  to  1.25  grammes  of  borax-glass,  and  a  covering  of  common 
salt.  The  fusion  is  continued  for  three-quarters  of  an  hour. 
When  the  operation  is  finished,  the  brittle  regulus  is  freed  from 
slag,  and  the  adhering  particles  of  slag  are  removed  by  washing. 
The  yield  by  this  assay  is  about  68  per  cent,  and  if  more  iron  is 
added,  it  will  appear  to  be  larger  on  account  of  the  contamination 
of  the  antimony  by  iron. 

Five  grammes  of  antimony  ore  are  mixed  in  a  crucible  (Fig.  49, 
p.  64)  with  10  grammes  of  anhydrous  potassium  ferrocyanide. 
The  mixture  is  covered  with  2.5  grammes  of  potassium  cyanide 
and  heated  to  a  cherry-red  heat.  The  yield  is  72  per  cent.1 — Or : 
10  grammes  of  ore,  and  40  to  50  grammes  of  potassium  cyanide, 
with  a  covering  of  common  salt,  are  fused  at  a  high  temperature. 
— Or:  100  parts  of  antimony  sulphide,  42  parts  of  iron  filings, 
10  parts  of  sodium  sulphate,  and  2  parts  of  powdered  wood 
charcoal  are  fused.  Yield  62  per  cent,  antimony. — Or:  100 
parts  of  antimony  sulphide,  80  parts  of  iron  slag,  50  parts  of 
sodium  carbonate,  and  10  parts  wood  charcoal.  Yield  60  per 
cent.  Impure  buttons  are  comminuted  and  treated  with  concen- 
trated nitric  acid,  filtered,  the  precipitate  of  antimonic  acid 
washed,  dried,  and  ignited  in  a  porcelain  crucible.  It  is  then 
weighed,  and  the  weight  found  multiplied  by  0.7922  gives  the 
metallic  antimony. 

2.  Roasting  and  reducing  assay. — The  ore,  which  is  very  fusi- 
ble, is  carefully  roasted  at  a  very  gradually  rising  temperature 
until  a  yellowish-white  powder  has  been  formed.  This  is  fused 
for  about  three-quarters  of  an  hour  with  the  same  or  double  the 
quantity  of  black  flux,  or  potassium  carbonate  and  flour,  with  a 
cover  of  common  salt.  If  necessary,  some  borax  is  added.  The 
yield  will  be  at  the  utmost  from  64  to  65  per  cent.  Sb.  Oxidized 
ores  do  not  require  roasting,  and  are  fused  with  3  parts  of  black 
flux  (with  1  part  of  argol),  1  part  of  sodium  carbonate,  and  15 
per  cent,  of  powdered  wood  charcoal,  at  not  too  high  a  tempera- 
ture :  or,  10  grammes  of  ore  with  25  grammes  of  black  flux  and 
1  part  of  argol  with  a  cover  of  salt. 

1  B.  u.  h.  Ztg.  1856,  p.  319. 


ANTIMONY — WET  ASSAYS.  245 

62.   WET  ASSAYS. 

Namely  : — 

1.  Gravimetric  assay. — 0.5  gramme  of  antimony  sulphide  is 
dissolved  in  aqua  regia,  some  tartaric  acid  added,  and  the  solu- 
tion filtered.  The  filtrate  is  saturated  with  ammonia  and  an 
excess  of  yellow  ammonium  sulphide,  and  digested  for  some 
time  on  the  water-bath.  It  is  then  filtered,  but  without  bringing 
the  precipitate  upon  the  filter.  This  is  again  digested  with 
ammonium  sulphide  and  then  filtered.  The  antimony  sul- 
phide is  thrown  down  out  of  the  filtrate  by  the  addition  of  di- 
luted hydrochloric  acid.  The  sulphuretted  hydrogen  is  driven 
off  on  the  water-bath,  and  the  liquid  then  filtered  upon  a  filter, 
previously  dried  at  100°  C.  (212°  F.),  weighed,  washed  with  sul- 
phuretted hydrogen  water,  and  the  precipitate  dried  at  100°  C. 
(212°  F.)  until  the  weight  remains  constant.  A  part  of  the  con- 
tents of  the  filter  is  then  weighed  off  in  a  small  porcelain  boat, 
placed  in  a  glass  tube,  and  heated  in  a  current  of  carbonic  acid 
gas  (Fig.  77,  p.  238),  in  order  to  remove  the  sulphur  in  excess, 
until  no  more  of  the  latter  escapes.  The  Sb2S3,  containing  71.8 
per  cent.  Sb,  is  weighed,  and  from  this  the  antimony  contained  in 
the  entire  mass  in  the  filter  is  calculated. 

Becker's  method.1 — Fuse  the  assay  material  with  3  parts  of 
sodium  or  potassium  carbonate  and  3  parts  of  sulphur.  Strongly 
sulphuretted  combinations  of  these  metals  are  thus  obtained.  They 
easily  give  off  sulphur  to  the  air,  and  when  decomposed  with  HC1 
large  quantities  of  sulphur  are  precipitated;  this  latter  circumstance 
interferes  greatly  with  the  subsequent  operations.  Donath2  ob- 
serves that  sodium  hyposulphite  completely  freed  from  water  by 
careful  melting  in  a  dish  and  finely  pulverized  is  much  better 
adapted  for  this  purpose.  In  this  case  disintegration  proceeds 
readily,  and  the  solution  lixiviated  from  the  fused  mass  shows  but  a 
slight  color.  From  this  solution  HC1  precipitates  the  respective 
sulphides  mixed  with  but  little  sulphur.  It  is  best  to  weigh  the 
antimonious  sulphide  as  such,  as  it  has  been  shown  by  Bunsen  that 

1  Ztschft.  f.  Anal.  Chera.  Bd.  17,  p.  185. 

2  Ztschft.  f.  Anal.  Chera.  Bd.  19,  p.  23. 


246  ASSAYING. 

an  accurate  determination  cannot  be  made  by  converting  it  into 
antimonic  oxide. 

2.  Volumetric  method. — The  antimony  sulphide  is  dissolved  in 
hydrochloric  acid,  and  heated  until  the  odor  of  sulphuretted  hy- 
drogen can  no  longer  be  detected.  Tartaric  acid,  or  potassium- 
sodium  tartrate  is  added,  and  the  solution  supersaturated  with  a 
cold  saturated  solution  of  sodium  bicarbonate  in  the  proportion 
of  about  20  cubic  centimeters  to  0.1  gramme  of  Sb2O3.  The  re- 
sult will  be  a  solution,  which,  on  the  addition  of  iodine,  will  be 
converted  into  antimonic  acid  and  hydriodic  acid,  SbHO2  -p  21 
-4-  H2O  =  SbHO3  +  2HI.  Starch  solution  is  now  added,  and  a 
sufficient  quantity  of  titrated  solution  of  iodine  to  color  the  fluid 
blue  is  allowed  to  drop  into  the  solution  from  a  burette.  A 
decinormal  solution  of  iodine  is  prepared  by  dissolving  12.7 
grammes  of  iodine  in  potassium  iodide,  and  diluting  this  to  the 
bulk  of  1  liter.  2  atoms  of  consumed  iodine  correspond  to  1 
molecule  of  antimony  oxide,  or  1  cubic  centimeter  of  solution  of 
iodine  to  0.0061  gramme  of  antimony.  The  standard  of  the  solu- 
tion of  iodine  is  determined  by  titration  with  tartar  emetic,  observ- 
ing the  same  conditions  regarding  the  concentration  and  quantity  of 
the  reagents  (tartaric  acid,  sodium  hydrocarbonate,  etc.)  in  the 
subsequent  titration. 

See  "  XIX.,  Sulphur,"  concerning  the  indirect  determination 
of  antimony  in  Sb2S3  by  the  quantity  of  sulphuretted  hydrogen 
evolved  therefrom. 

WeiVs  method  of  determining  antimony  with  protochloride  of 
tin. — If  nothing  but  the  antimony  is  to  be  determined  in  the  assay, 
treat,  according  to  the  richness  of  the  assay  material,  from  2  to  5 
grammes  in  aqua  regia  and  excess  of  HC1;  add  potassium  perman- 
ganate until  the  solution  retains  a  rose  color,  boil  until  the  rose 
color  disappears  and  potassium  iodide  starch-paper  is  no  longer 
colored  blue  by  the  escaping  vapors.  The  solution  thus  obtained 
contains  the  antimony,  as  antimonic  acid.  Dilute  to  £  liter  with  an 
aqueous  solution  of  tartaric  acid.  Take  25  c.c.  of  this  solution  for  the 
assay,  and  add  a  measured  quantity  of  cupric  sulphate  solution  con- 
taining a  known  amount  of  copper.  Heat  mixture  to  boiling  and  add 
25  c.c.  of  concentrated  HC1,  then  titrate  the  boiling  solution  with 
protochloride  of  tin  until  discoloration  takes  place.  The  number 


ANTIMONY — WET   ASSAYS.'  247 

c.c.  of  protochloride  of  tin  which  corresponds  to  the  amount  of  the 
copper  salt  added  must  be  known  ;  the  number  of  c.c  of  protochloride 
of  tin  used  over  this  amount  corresponds  to  the  amount  of  anti- 
mony. By  calculating  the  amount  of  copper  corresponding  to  this 
volume  and  multiplying  the  result  by  0.96214,  we  get  the  content 
of  antimony  in  the  assay  material 

SbCl5-fSnCla=SnCl4-fSbCl3 

and  2CuCl-|-SnCl2=SnCl4-f-2CuCl,  hence  1  equivalent  of  antimony 
corresponds  to  2  equivalents  of  copper,  also 

_§JL  =  122-— 0.96214 
2Cu      126.4 

the  results  can  be  more  quickly  obtained  by  the  use  of  the  following 
table :— 


248 


ASSAYING. 


Titer  of  the 
protochloride 
of  tin  solution, 
in  cubic 
centimeters, 
for  0.1  gramme 
of  copper. 

Cubic  centimeters  of  protochloride  of  tin  solution  used  for  every 
25  cubic  centimeters  of  assay  solution  (2  grammes 
=  250  cubic  centimeters)  correspond  to 
per  cent,  of  antimony. 

1 

2 

3 

4 

5 

6 

7 

8           9 

10 

15.0 

3.20 

6.40 

9.61 

12.81 

16.01 

19.22  122.42 

25.63  28.83  132.03 

15.1 

18 

36 

55 

73 

15.92 

10 

29 

47 

66  31.84 

15.2 

15 

31 

46 

62 

77 

18.93 

09 

24 

40 

55 

15.3 

13 

27 

40 

54 

68 

81 

21.95 

09 

22 

36 

15.4 

11 

23 

35 

46 

58 

70 

82 

24.93 

05 

17 

15.5 

09 

19 

29 

39 

49 

58 

68 

78 

27.88 

30.98 

15.6 

07 

15 

23 

31 

39 

47 

55 

63 

70 

78 

15.7 

05 

11 

17 

23 

29 

35 

41 

47 

53 

59 

15.8 

04 

08 

12 

16 

20 

24 

28 

32 

36 

40 

15.9 

02 

04 

06 

09 

11 

13 

16 

18 

20 

23 

16.0 

00 

00 

00 

00 

00 

01 

01 

01 

01 

01 

16.1 

2.98 

596 

8.94 

11.93 

14.91 

17.89 

2092 

23.86 

26.84 

29.82 

16.2 

96 

92 

88 

85 

81 

77 

74 

70 

66 

63 

16.3 

94 

88 

83 

77 

72 

66 

60 

55 

49 

44 

16.4 

92 

84 

77 

69 

62 

54 

47 

39 

32 

24 

16.5 

91 

83 

74 

66 

57 

49 

30 

32 

23 

15 

16.6 

89 

79 

68 

58 

48 

37 

29 

16 

06 

28.96 

16.7 

87 

75 

62 

50 

38 

25 

13 

01  i'25.88 

76 

16.8 

85 

71 

57 

43 

•  28 

14 

00 

22.86 

71 

57 

16.9 

83 

67 

51 

35 

19 

02  19.86 

70 

54 

38 

17.0 

82 

65 

48 

31 

14 

16.97 

79 

62 

45 

28 

17.1 

80 

61 

42 

23 

04 

85 

66 

47 

28 

09 

17.2 

79 

58 

37 

16 

13.95 

74 

53 

32 

11 

27.90 

17.3 

78 

56 

34 

12 

90 

68 

46 

24 

02 

80 

17.4 

76 

52 

28 

04 

80 

56 

32 

09 

24.85 

61 

17.5 

74 

48 

22 

10.96 

70 

45 

19 

21.93 

67 

41 

17.6 

73 

46 

19 

92 

66 

39 

12 

85 

59 

32 

17.7 

71 

42 

13 

85 

56 

27  18.99 

70 

41 

33 

17.8 

70 

40 

11 

81 

51 

22 

92 

62 

33 

03 

n.9 

68 

36 

05 

73 

42 

10 

79 

47 

15 

26.84 

18.0 

66 

33 

7.99 

66 

32 

15.99 

65 

32 

23.98 

65 

18.1 

65 

31 

96 

62 

27 

93 

58 

24 

89 

55 

18-2 

62 

25 

87 

50 

13 

75 

38 

00 

73 

26 

18.3 

61 

23 

85 

47 

08 

70 

32 

20.94 

55 

17 

18.4 

60 

21 

82 

42 

03 

64 

25 

85 

46 

07 

18.5 

59 

19 

79 

39 

12.98 

58 

18 

78 

37 

25.97 

18.6 

58 

17 

76 

35 

94 

52 

11 

70 

29 

88 

18.7 

56 

13 

70 

27 

84 

41  17.98 

55 

12 

68 

18.8 

55 

11 

67 

22 

79 

35 

91 

47 

03 

59 

]8.9 

54 

08 

62 

16 

70 

24 

78 

32 

22.86 

40 

19.0 

52 

06 

59 

12 

65 

18 

71 

24 

77 

30 

19.1 

51 

02 

53 

04 

55 

06 

57 

08 

54 

11 

19.2 

50 

00 

50 

00 

50 

00 

51 

01 

51 

01 

19.3 

49 

4.98 

47 

9.96 

45 

14.95 

44 

19.93 

42 

24.91 

19.4 

47 

94 

41 

89 

36 

83 

30 

78 

25 

72 

19.5 

46 

92 

38 

85 

31 

77 

24 

70 

16 

63 

19.6 

45 

90 

35 

81 

26 

72 

17 

62 

08 

53 

19.7 

43 

86 

30 

73 

17 

60 

03 

47  21.90 

34 

19.8 

42 

84 

27 

69 

12 

54  16.97 

39 

82 

24 

19.9 

41 

82 

24 

66 

07 

49 

90 

32 

73 

14 

20.0 

40 

81 

21 

62 

02 

43 

83 

24 

64 

05 

ANTIMONY — WET  ASSAYS.  249 

The  simultaneous  presence  of  iron,  copper,  and  antimony  can 
also  be  very  quickly  anil  sharply  determined  by  means  of  proto- 
chloride  of  tin.  Dissolve  in  aqua  regia,  pass  H3S  through  solu- 
tion, filter,  oxidize  in  the  filtrate  with  potassium  chlorate,  add  HC1, 
and  after  filling  up  to  the  £  liter  mark  titrate  the  iron.  Dissolve 
the  precipitated  metallic  sulphides  in  aqua  regia,  evaporate  consid- 
erably, and  after  adding  HC1  and  filling  up  to  £  liter  mark,  simul- 
taneously titrate  the  copper  and  antimony,  allow  the  titrated  solu- 
tion to  stand  over  night,  whereby  the  copper  alone  becomes  com- 
pletely reoxidized,  and  the  next  day  titrate  the  copper  alone.  The 
difference  in  the  quantity  consumed  corresponds  to  the  antimony. 
The  number  of  c.c.  used  in  titrating  the  iron  multiplied  by  0.883 
give  its  content. 

Volumetric  estimation  of  antimony  in  the  presence  of  tin.1 — 
This  method  is  applicable  to  alloys  such  as  Britannia  metal  or  type 
metal,  and  depends  upon  the  fact  that  antimonic  chloride  is  reduced 
to  antimonious  chloride  by  hydriodic  acid,  with  the  constant  libera- 
tion of  iodine,  whilst  the  stannic  chloride  is  unreduced.  Dissolve 
the  finely-divided  alloy  in  strong  HC1,  and  add  from  time  to  time 
small  quantities  of  potassium  chlorate.  After  all  the  metal  is  dis- 
solved and  the  antimonious  chloride  converted  into  antimonic 
chloride,  the  solution  is  gently  boiled  until  all  the  oxides  of  chlo- 
rine have  been  expelled.  Cool,  and  add  a  slight  excess  of  a  strong 
solution  of  potassium  iodide.  The  free  iodine  is  then  estimated  by 
a  standard  solution  of  sodium  hyposulphite.  Since  122  parts  of 
antimony  liberate  254  parts  of  iodine,  the  amount  of  iodine  found 
multiplied  by  0.48031  will  give  the  amount  of  antimony  present. 

3.  Electrolytic  determination  of  antimony. — According  to  Parodi 
and  Mascazzini,2  antimony  can  be  separated  in  a  compact  form  from 
a  solution  of  the  chloride  in  ammonium  tartrate,  or  from  its  sulpho- 
salt.  According  to  Luckow,3  this  precipitate  from  the  trichloride  is 
of  a  pale-gray  color  and  has  a  metallic  lustre.  It  dissolves  with 
difficulty  in  HC1,  but  readily  in  HNO3,  especially  after  moistening 
with  HC1. 

According  to  Classen,  antimony  can  be  precipitated  from  a  HC1 
solution,  but  the  metal  does  not  adhere  with  sufficient  tenacity  to 

1  Chem.  News,  xlv.,  p.  101. 

2  Gazz.  Chimikal,  8. 

a  Ztschft.  f.  Anal.  Chem.,  Bd.  18,  p.  588. 


250  ASSAYING. 

the  electrode,  even  if  potassium  oxalate  has  been  added.  An  ad- 
herent metallic  deposit  can  be  obtained  by  adding  potassium  tar- 
trate,  but  the  separation  is  then  too  slow.  The  precipitation  of  an- 
timony from  its  sulpho-salts  is  complete  and  satisfactory.  If  am- 
monium sulphide  is  used  to  produce  a  double  salt,  it  must  contain 
neither  free  ammonia  nor  polysulphides.  When  a  sulpho-salt  is  used 
0.2  gramme  of  the  assay  material  is  melted  at  a  moderate  heat, 
with  four  times  its  weight  of  a  mixture  of  soda  and  sulphur.  Lix- 
iviate with  water,  filter,  pour  hot  yellow  ammonium  sulphide  re- 
peatedly over  the  residue  upon  the  filter,  wash  with  water,  and 
subject  the  cold  filtrate  to  the  action  of  the  electric  current.  When 
a  solution  of  antimony  containing  ammonium  sulphide  is  electro- 
lyzed,  there  is  formed  over  the  metal  a  coating  of  sulphur  which 
cannot  be  washed  off  with  water.  After  the  metal  is  washed  with 
alcohol,  however,  the  thin  coating  of  sulphur  can  be  rubbed  off  with 
the  finger,  or  a  handkerchief  moistened  with  alcohol,  without 
danger  of  loss.  A  separation  of  antimony  sulphide  will  be  ob- 
served in  the  positive  electrode,  but  it  will  again  be  reduced  if  an 
excess  of  ammonium  sulphide  is  present.  Alkaline  polysulphides 
should  not  be  present,  as  they  impair  the  accuracy  of  the  results. 
Classen  and  Ludwig1  have  found  that  polysulphides  are  converted 
by  hydrogen  dioxide  into  sulphates  in  the  same  manner  as  mono- 
sulphides.  They  therefore  recommend  fusing  the  precipitate,  con- 
taining the  antimony  and  lead,  in  the  form  of  sulphides,  with  ten 
times  its  weight  of  dehydrated  sodium  hyposulphide,  lixiviating  with 
water,  and  heating  solution  in  a  carefully  cleaned  platinum  dish  with 
ammoniacal  hydrogen  dioxide  until  the  solution  has  become  color- 
less, or  a  precipitate  of  antimonious  sulphide  has  formed.  Add  10 
c.c.  of  a  concentrated  solution  of  sodium  monosulphide  and  the 
cold  solution  electrolyzed  with  a  current  of  1.5  to  2  c.c.  of  oxyhy- 
drogen  gas  per  minute.  A  battery  of  5  or  6  Meidinger  cells  is  best 
adapted  for  the  purpose.  Precipitation  is  complete  in  10  or  12 
hours,  the  precipitate  is  washed  with  water  and  alcohol,  dried  for  a 
short  time  at  80°  or  100°  C.,  and  weighed. 

1  Berichte  der  deutsch.  chem.  Gresellschaft,  1885,  Bd.  18,  p.  1104.     Chemi- 
kerztg,  1885,  p.  891. 


ARSENIC — FIRE   ASSAYS.  251 

XIV,  ARSENIC. 

63.    ORES. 

Native  arsenic,  mispickel,  FeAsS,  with  46  As;  leucopyrite, 
Fe2As3,  with  66.8  As ;  nickel  and  cobalt  ores,  etc. 

64.    FIRE    ASSAYS. 

The  object  of  these  is  to  determine  the  quantity  of  arsenic,  or 
of  its  compounds,  which  may  be  obtained  from  the  ores. 

A.  Native  arsenic. — 300  to  500  grammes  of  mispickel  or  leu- 
copy  rite  (when  arsenious  acid  is  present  the  ores  are  mixed  with  16 
to  20  per  cent,  powdered  charcoal,  and  with  potassium  carbonate 
in  case  metallic  sulphides  should  be  contained  in  the  ore)  are  in- 
troduced into  a  clay  tube,  one  end  of  which  is  closed.     A  spiral 
of  sheet  iron  is  placed  in  the  open  end,  and  the  tube  is  closed  by 
a  sheet-metal  cap,  which  is  loosely  luted  on.     The  tube  is  then 
brought  into  the  furnace,  and  the  charge  is  gradually  heated  for 
one  to  one  and  a  half  hours  at  a  red  heat,  the  end  with  the  spiral 
projecting  from  the  furnace.     When  the  operation  is  finished,  the 
tube  is  allowed  to  cool,  and  is  taken  out.    The  sheet-iron  spiral  is 
then  removed  and  unrolled,  and,  if  the  operation  has  been  con- 
ducted at  the  proper  temperatures,  scales  of  white  flaky  arsenic 
and  some  gray  powder,  both  allotropic  modifications  of  arsenic, 
will  fall  off.     The  product  is  then  weighed  (FeAsS  =  FeS  -f  As 
and  Fe2As3  =  2FeAs  +  As). 

White  metallic  scales  will  be  the  result,  when  the  receiver  is 
small  and  has  nearly  the  same  temperature  as  that  of  the  arseni- 
cal vapors ;  and  gray  powder,  when  the  receiver  is  large  or  has  a 
decidedly  lower  temperature  than  that  of  the  arsenical  vapor,  and 
when  it  is  evolved  along  with  other  heated  gases  (as  in  the  reduc- 
tion of  arsenious  acid  by  charcoal). 

B.  Arsenious  acid. — 2  to  5  grammes  of  ore  are  placed  in  the 
open  end  of  a  refractory  glass  tube,  the  other  end  of  which, 
somewhat  drawn  out  and  bent  in  a  right  angle,  projects  into  a 
large    Woulff  bottle.     The  end  of  the  tube  containing  the  ore  is 
laid  so  as  to  incline  somewhat  upwards,  in  a  combustion  furnace 


252  ASSAYING. 

(Fig.  77,  p.  238),  and  heated.  The  Woulff  bottle  is  connected 
with  an  aspirator,  when  the  arsenious  acid  will  deposit  itself  in 
the  straight  and  curved  part  of  the  tube,  and  in  the  Woulff 
bottle.  It  is  driven  by  heating,  from  the  horizontal  to  the  bent 
part  of  the  tube ;  this  is  cut  off,  the  arsenious  acid  is  wiped  out 
with  a  feather,  and  then  weighed  together  with  that  contained 
in  the  bottle. 

C.  Realgar  (red  orpiment),  with  70.03  As,  and  yellow  orpi- 
ment,  As2S3,  with  60.9  As. — The  object  of  the  docimastic  tests  is 
to  determine  the  quantity  of  orpiments  which  can  be  prepared 
from  the  raw  materials  in  question,  or  to  ascertain  the  propor- 
tions of  these  to  be  added  in  certain  technical  processes. 

1.  Assays  for  the  determination  of  realgar. — Iron  pyrites  (7FeS2 
—  FeS2  +  6FeS  -f  68  «=  23  per  cent.  S)  and  arsenical  pyrites 
(FeAsS  =  FeS  +  As  =  46  per  cent.  As)  in  different  proportions 
(20  to  30  grammes,  or  more)  are  heated  in  a  glass  tube  closed  at 
one  end,  or  in  a  glass  retort,  whereby  realgar  is  sublimed.     This 
is  fused  in  a  porcelain  crucible,  and  its  color  examined.     Lighter 
or  darker  shades  can  be  given  to  the  color  by  adding,  respectively, 
sulphur  or  arsenic. 

2.  Assays  for  the  determination  of  yellow  orpiment. — A  mixture 
of  arsenious  acid  with   sulphur  (together   10   to   20  grammes) 
in  different  proportions  is  heated  (generally  with  6  to  12  per  cent, 
of  sulphur,  or  less)  in  a  glass  retort  at  a  gradually  rising  tempe- 
rature, until  the  sublimation  of  the  yellow  product  is  complete. 

While  the  native  yellow  orpiment  is  a  combination  of  As2S3, 
difficult  to  dissolve  in  acids,  the  artificial  product  consists  princi- 
pally of  arsenious  acid  colored  by  a  few  per  cent,  of  arsenic 
sulphide,  and  is  consequently  very  poisonous. 

65.   WET  ASSAYS. 

These  may  be — 

A.   Gravimetric  assays. 

1.  Wet  assay. — \  to  1  gramme  of  ore  is  ignited  in  a  porcelain 
crucible  at  a  strong  red  heat,  with  4  to  5  times  the  quantity  of 
saltpetre,  and  1J  times  the  quantity  of  calcined  sodium  carbo- 
nate, with  a  thick  covering  of  these  fluxes.  When  the  crucible  is 


ARSENIC — WET  ASSAYS.  253 

cold,  the  potassium  arseniate  is  extracted  by  lixiviation  with  hot 
water,  and  evaporated  to  dryness  with  nitric  acid.  The  dry  mass 
is  treated  with  water,  the  silicic  acid  filtered  off ;  the  filtrate  is 
treated  with  ammonia  in  excess,  then  with  a  solution  of  magne- 
sium sulphate  (or  at  once  with  magnesia  mixture  prepared  from 
110  parts  of  crystallized  magnesium  chloride,  700  parts  concen- 
trated ammonia,  140  parts  ammonium  chloride,  and  1300  parts 
water).  The  liquid  is  allowed  to  stand  for  12  hours,  the  ammo- 
nium-magnesium arseniate,  2(MgNH4.  AsO4)  +  H2O,  is  filtered  off 
upon  a  filter  previously  dried  at  100°  C.  (212°  F.),  and  weighed ; 
100  parts  of  salt  dried  at  100°  C.  (212°  F.)  and  weighed,  will 
contain  60.51  parts  of  arsenic  acid,  corresponding  to  65.21  per 
cent,  of  arsenic  and  86.08  per  cent,  of  arsenious  acid.  By  ignit- 
ing very  carefully  and  not  too  quickly,  the  magnesium  salt  passes 
into  Mg2As2O7.  Or  the  sample  is  digested  in  strong  nitric  acid 
with  the  addition  of  a  few  crystals  of  potassium  chlorate.  The 
solution  is  diluted  with  water  and  filtered.  Some  lead  nitrate  in 
solution  is  added  to  the  acid  liquid,  when  lead  sulphate  will  be 
separated,  lead  arseniate  remaining  in  solution.  The  precipitate 
of  lead  sulphate  is  filtered  off,  the  filtrate  saturated  with  soda, 
when  the  lead  arseniate  will  be  separated.  This  is  filtered  off, 
washed,  dried,  and  weighed.  100  parts  arseniate  =  22.2  parts  of 
metallic  arsenic,  or  29  parts  of  arsenious  acid. 

2.  Wet  method  combined  with  the  dry.1 — 1  'to  1  \  grammes  of  the 
substance  is  fused  in  the  manner  indicated  under  1 ,  wTith  saltpe- 
tre and  sodium  carbonate,  in  order  to  obtain  a  solution  of  alka- 
line arseniate.  The  filtrate  is  saturated  with  nitric  acid,  and 
strongly  diluted  in  case  sulphuric  acid  is  present.  Silver  nitrate 
in  excess  is  then  added,  and  sufficient  ammonia  to  cause  the  pre- 
cipitate to  disappear.  The  excess  of  ammonia  is  evaporated 
without  boiling  until  its  odor  has  disappeared.  The  silver  arse- 
niate is  then  filtered  off,  dried,  and  smelted  with  lead,  and  the 
arsenic  calculated  from  the  quantity  of  silver  found,  1  atom  of 
arsenic  being  precipitated  to  3  atoms  of  silver,  or  100  silver 
corresponds  to  23.15  arsenic  =  35.5  arsenic  acid. 

1  Plattner-Ritcher's  Lothrohprobirkunst,  1878,  p.  651. 


254  ASSAYING. 

B.  Volumetric  assays. — The  method  most  used  is  T.  J/bArV 
estimation  of  arsenious  acid;  according  to  which  arsenious  acid 
combined  with  soda  is  completely  converted  into  arsenic  acid  by 
iodine  (As2O3  +  2I2  +  2Na2O  «  4NaI  +  As2O5). 

A  solution  containing  500  cubic  centimeters  2.5  grammes  of 
iodine  and  4  grammes  potassium  iodide,  or  in  1  c.c.  0.005 
gramme  of  iodine,  is  added  to  a  solution  containing  sodium  arse- 
nite,  sodium  bicarbonate,  and  some  starch  paste.  Fixing  of  the 
standard :  4.95  grammes  of  arsenious  acid  are  placed  in  a  flask 
and  dissolved  in  sodium  bicarbonate,  in  about  200  cubic  centime- 
ters of  water.  The  clear  solution  is  poured  oif,  and  sodium  salt 
and  water  are  added  in  small  portions  until  solution  is  complete. 
It  is  then  transferred  to  a  liter  flask,  20  to  25  grammes  more  of 
sodium  bicarbonate  are  then  added,  and  the  flask  is  filled  up  to 
the  mark.  10  c.cm.  of  this  solution  are  taken,  some  fresh  starch 
solution  and  sodium  bicarbonate  added,  the  liquid  diluted  to 
about  150  c.c.,  and  then  titrated  with  the  solution  of  iodine 
until  the  blue  color  appears,  which  must  not  disappear  even  when 
sodium  bicarbonate  is  added.  Arsenic  acid  must  be  reduced  to 
arsenious  acid  by  introducing  sulphurous  acid  gas  into  the  hot 
acid  solution,  or  by  the  addition  of  sulphites. 

Pearce's  method  of  determining  arsenic.2 — The  finely  powdered 
assay  material  is  mixed  in  a  porcelain  crucible  with  six  to  ten  times 
its  weight  of  a  mixture  of  equal  parts  of  carbonate  of  sodium  and 
nitrate  of  potassium.  The  mass  is  then  heated  with  a  gradually 
increasing  temperature  to  fusion,  and  kept  for  a  few  minutes  in 
that  state.  Lixiviate  with  water,  filter,  and  wash  with  hot  water. 
The  arsenic  is  in  the  filtrate  as  alkaline  arseniate.  Acidify  the  fil- 
trate with  HN03,  and  boil  to  expel  excess  of  carbonic  acid  and 
nitrous  fumes.  Exactly  neutralize  by  alternate  additions  of  ammonia 
and  HN03.  If  the  neutralization  has  caused  a  precipitate,  it  is  best 
to  filter  off  at  once.  A  solution  of  nitrate  of  silver  is  now  added 
in  slight  excess  and  stir  vigorously.  Filter  and  wash  thoroughly 
with  cold  water.  Dissolve  on  filter  the  arseniate  of  silver  with  dilute 
HN03.  Cool  and  add  about  5  c.c.  of  ferric  sulphate.  Titrate  with 

1  Mohr,  Titrirmethode,  1874. 

2  Pro.  Colorado  Scientific  Society,  vol.  i.     Engineering  and  Mining  Journ. 
May  5,  1883,  p.  256. 


URANIUM — WET  ASSAYS.  255 

a  standardized  solution  of  ammonium  sulpho-cyanide  until  a  faint 
red  tinge  is  obtained  which  remains  after  considerable  shaking. 
From  the  formula  3Ag2O.As206  we  deduct  648  parts  Ag  =  150 
parts  As,  or  Ag  :  As=  108  :  25.  Canby1  simplifies  this  method 
by  neutralizing  with  oxide  of  zinc  instead  of  ammonia,  obtaining 
quite  as  satisfactory  results  and  a  great  saving  of  time.  The  oxide 
of  zinc  is  added  in  excess,  and  as  it  seems  to  hold  the  gelatinous 
silica  and  alumina,  which  are  usually  precipitated  upon  neutralizing, 
the  washing  of  the  precipitated  arseniate  of  silver  is  usually  much 
more  rapid. 

Arsenic  in  glass.2 — Fresenius  finds  that  many  samples  of  glass 
contain  arsenic  which  under  some  circumstances  may  be  set  free  and 
cause  errors.  When  an  alkaline  flux  is  melted  in  contact  with  an  ar- 
seniferous  glass,  either  in  a  current  of  carbonic  acid  or  hydrogen,  the 
arsenic  will  be  set  free.  By  the  reducing  action  of  hydrogen  alone 
the  amount  set  free  is  small.  If  a  solution  of  an  alkaline  carbonate 
be  boiled  in  a  vessel  of  such  glass,  a  very  perceptible  amount 
of  arsenic  will  be  taken  into  solution,  while,  on  the  other  hand,  HC1 
solutions  have  no  solvent  effect.  The  glass  used  in  the  above  ex- 
periment contained  0.20  per  cent,  of  arsenic. 


XV,  URANIUM, 

66.    ORES. 

Pitch  blende,  Ur3O8,  with  84.9  Ur. 

67.    WET   ASSAYS. 

^Namely : — 

A.   Gravimetric  assays. 

1.  More  accurate  analytical  process. — 1  to  2  grammes  of  ore, 
etc.,  are  decomposed  with  concentrated  nitric  acid.  The  solu- 
tion is  diluted  and  the  residue  and  precipitate  (silicic  acid, 
lead  sulphate,  basic  antimony,  and  bismuth  salts)  are  filtered 
off.  The  arsenic  acid  in  the  filtrate  is  reduced  by  means  of 
sulphurous  acid  to  arsenious  acid,  and  the  sulphurous  acid 
removed  by  boiling.  It  is  then  precipitated  with  sulphuretted 

1  Trans.  Am.  Inst.  M.  E.  vol.  XVII.,  p.  77. 

2  Ztschft.  f.  Anal.  Chem.  Bd.  22,  p.  397. 


256  ASSAYING. 

hydrogen  (As,  Sb,  Pb,  Bi,  Cu),  filtered,  and  the  sulphu- 
retted hydrogen  removed  by  boiling.  The  iron  is  then  oxidized 
by  potassium  chlorate,  ammonium  carbonate  in  excess  added,  and 
the  liquid  filtered.  Ammonium  sulphide  is  now  cautiously  added 
in  the  cold  in  order  to  precipitate  Mn,  Zn,  Ni,  Co,  leaving  the 
uranium  in  solution.  The  liquid  is  then  filtered,  and  the  filtrate 
heated  with  nitric  acid  to  separate  sulphur.  It  is  now  again 
filtered,  and  when  the  solution  has  become  cold  the  uranium  is 
precipitated  as  brownish-yellow  ammonia-uranic  oxide,  by  am- 
monia. This  is  filtered  off,  washed,  dried,  and  ignited  to  green 
uranoso-uranic  oxide  (UrO2.2UrO3  =  Ur3O8),  with  84.8  ura- 
nium, corresponding  to  96.22  uranous  oxide  (UrO2)  and  101.9 
uranic  oxide  (UrO3). 

2.  Patera's  technical  test.1 — 5  grammes  of  ore  are  dissolved  in 
nitric  acid,  not  in  excess.  The  unfiltered  solution,  which  has 
been  freed  from  the  excess  of  nitric  acid  by  boiling,  is  super-satu- 
rated with  sodium  carbonate,  boiled  for  a  short  time,  and  the  so- 
lution containing  the  sodic-uranic  carbonate  is  filtered  into  a 
golden  dish.  The  solution  is  evaporated  to  dry  ness,  the  residue 
ignited  and  extracted  with  hot  water,  and  the  insoluble  acid 
sodium  uranate  (Ur4Na2O7)  is  filtered  off,  ignited,  and  weighed. 
100  parts  of  the  weight  obtained  equal  88.3  parts  of  uranoso- 
uranic  oxide. 

In  case  a  golden  capsule  should  not  be  at  hand,  the  solution  of 
the  uranic  oxide  in  soda  is  treated  with  sodium  hydrate  in  order 
to  precipitate  hydrated  acid  sodium  uranate.  It  is  then  filtered, 
washed,  and  dried,  and  the  precipitate  is  removed  as  much  as 
possible  from  the  filter  and  ignited  together  with  the  ash  of  the 
filter.  It  is  then  again  washed  upon  the  filter,  .dried,  and 
ignited.  In  case  a  considerable  quantity  of  copper  is  present,  a 
small  quantity  of  it  passes  into  the  alkaline  solution. 

According  to  Alibegoff,2  uranium  cannot  be  separated  from  cal- 
cium by  means  of  ammonium  sulphide,  but,  if  present  in  the  solu- 
tion as  chloride,  it  is  completely  precipitated  by  mercurous  oxide. 
To  completely  precipitate  uranium  iii  the  presence  of  alkaline  earths 

1  Dingier,  clxxx.  242  (Patera).     Fresenius's  Ztschr.  v.  229  (Fresenius)  ; 
viii.387  (Winkler). 

2  Liebig's  Anal.  d.  Chem.  1886,  Bd.  233,  p.  143. 


URANIUM — WET  ASSAYS.  257 

it  is  recommended  to  add  sufficient  ammonium  chloride  to  the  solu- 
lution  containing  the  chlorides,  and,  after  maintaining  it  at  a  boiling 
temperature  for  some  time,  to  add  pure  mercurous  oxide.  The 
solution  is  then  agitated,  and  after  boiling  once  more  decanted.  In 
the  presence  of  many  alkaline  earths  it  is  several  times  boiled  with 
water  containing  ammonium  chloride,  filtered  and  washed  with  cold 
water  also  containing  ammonium  chloride.  Small  particles  of  al- 
kaline earths  which  may  still  adhere  to  the  olive  green  uranic  oxide 
after  ignition  are  recognized  by  their  yellow  color.  The  precipitate 
and  filter  must  be  carefully  ignited  in  a  closed  platinum  crucible, 
then  in  an  open  crucible,  and  finally  over  a  blast  lamp.  The  sepa- 
ration of  the  uranium  from  barite  (BaS04)  being  incomplete  it  is 
advisable,  if  the  latter  be  present,  previously  to  separate  it  with 
HS04. 

I>.  Volumetric  assay.1 — 1  to  2  grammes  of  ore  is  dissolved  in 
concentrated  sulphuric  acid.  The  sulphuric  acid  (not  hydro- 
chloric acid)  solution  is  diluted  according  to  the  richness  of  the 
ore,  to  J  or  J  liter.  50  cubic  centimeters  of  this  are  taken, 
placed  in  a  suitable  flask,  and  diluted  with  100  cubic  centi- 
meters of  water.  The  liquid  is  boiled  for  half  an  hour  with 
zinc  until  the  yellow  solution  of  uranic  oxide  has  assumed  the 
sea-green  color  of  uranous  oxide.  All  the  zinc  is  dissolved, 
and  the  uranous  oxide  is  titrated  with  potassium  permanganate 
(p.  123).  Uranous  oxide  requires  the  same  quantity  of  potassium 
permanganate  to  become  oxidized,  as  ferrous  oxide. 

According  to  Zimmermann,2  the  oxysalts  of  uranium  cannot 
well  be  determined  in  HC1  solution  on  account  of  their  being  con- 
verted into  uranous  subchloride  (Ur4Cl3),  which  is  a  very  unstable 
compound.  The  determination  of  uranium  in  HC1  solution  is  there- 
fore made  by  destroying  the  injurious  influence  of  the  HC1  by  the 
addition  of  manganous  sulphate  and  excluding  the  air  in  titrating. 
It  is  consequently  best  to  reduce  the  uranium  compound  in  a  flask 
with  zinc  and  HC1,  the  air  being  excluded.  At  first  the  solution 
becomes  green,  but  later  a  dirty  green,  then  brown,  and  finally  a 

1  Journ.  f.  prakt.  Chem.  xcix.  231  (Belohoubeck).     Fresenius's  Ztschr.  xi. 
179  ;  xvi.  104.     Gouyard's  Probe  in  Cliem.  Centr.  1864,  p.  339.— Analyse  der 
Uranoxydalkalien  in  Fresenius's  Ztschr.  iii.  71  (Stolba). 

2  Liebig's  Anal.  d.  Chem.  Bd.  213,  p.  285. 

17 


258  ASSAYING. 

beautiful  red.  When  the  latter  color  remains  constant  the  reaction 
is  finished.  In  the  meanwhile  a  known  excess  of  permanganate  is 
placed  in  a  porcelain  dish,  strongly  acidulated  with  H2S04,  and 
manganous  sulphate  added ;  the  hot  solution  of  uranous  subchloride 
is  then  quickly  added.  The  excess  of  permanganate  is  then  removed 
by  a  solution  of -ferrous  oxide  (whose  titer  with  permanganate  is 
known)  and  the  excess  of  it  added  measured  back  into  the  same  per- 
manganate until  the  appearance  of  a  slight  rose  color. 

Method  of  determining  uranium  with  potassium  dichromate  and 
iodine. — According  to  Zimmermann,1  this  method  is  executed  by 
acidulating  the  reduced  oxysalt  with  HC1  and  adding  an  excess  of 
potassium  dichromate  solution  of  known  strength,  whereby  the  ura- 
nous oxide  is  converted  into  uranic  oxide.  Dilute  with  water  to 
150  c.c.  and  add,  with  constant  stirring,  a  solution  of  potassium 
iodide  whereby  iodine  is  separated  from  the  bichromate  remaining 
in  excess.  After  adding  starch  paste  this  iodine  is  determined  with 
a  solution  of  sodium  hyposulphate  of  known  strength.  The 
titrated  iodine  solution  is  finally  added,  drop  by  drop,  until  the 
liquid  has  acquired  a  very  slight  blue  color.  If  uranous  subchloride 
is  to  be  determined,  the  reduced  solution  is  allowed  to  run  into  an 
excess  of  potassium  chromate  solution  mixed  with  HC1 ;  the  pro- 
cess otherwise  is  the  same  as  above. 


XVI,  TUNGSTEN, 

The  only  important  tungsten  mineral  is  wolfram,  which  is  es- 
sentially FeWo4,  but  always  containing  more  or  less  manganese. 
In  the  pure  state  it  contains  76.4  per  cent,  tungstic  acid  or  60.5  per 
cent,  metallic  tungsten.  Wolfram  is  brownish-black,  gives  a  red- 
dish-brown or  blackish-brown  streak.  It  fuses  before  the  blowpipe 
to  a  magnetic  globule;  with  borax  it  gives  the  iron  reaction;  with 
soda  upon  platinum  foil  the  manganese  reaction.  Next  to  gold  and 
platinum  metallic  tungsten  is  specifically  the  heaviest  metal  (17.0  to 
17.6).  It  is  very  hard  and  brittle,  has  a  color  and  lustre  of  iron 
and  remains  unchanged  in  the  air,  but  ignites  when  heated  in  a 
finely  divided  state  and  burns  to  tungstic  acid.  It  is  very  refractory 
and  has  never  as  yet  been  fused  by  itself.2 

1  Ztschft.  f.  Anal.  Chem.  Bd.  23,  p.  65. 

2  Fortschritte  im  Probirwesen.     Balling,  Berlin,  1887,  p.  162. 


TUNGSTEN — WET   ASSAYS.  259 

68.    FIRE  ASSAY. 

By  melting  wolfram  in  crucibles  lined  with  charcoal  at  a  very 
high  temperature,  a  hard,  brittle,  foliated  regulus  resembling  white 
pig  iron  is  obtained,  which  contains  tungsten,  manganese,  and  iron, 
and  whose  content  of  tungsten  can  only  be  determined  in  the  wet 
way. 

69.    WET  ASSAYS. 

A.   Gravimetric  assays. 

1.  Sheele's  method. — The  very  finely  pulverized  wolfram  is  several 
times  evaporated  to  dryness  with  an  excess  of  HC1  to  which  some 
HN03  is  finally  added.     The  lumps  that  form  are  carefully  crushed 
before  each  addition  of  HC1  and  the  dish  heated  to  120°C.  in  an 
air  bath.     The  final  residue  is  treated  with  water  acidulated  with 
HC1  and  the  separated  tungstic  acid  filtered  off,  ignited,  and  weighed. 
The  digestion  must  be  continued  until  the  brown  tungsten  powder 
is  converted  into  yellow  tungstic  acid.     If  the  ore  is  not  entirely 
pure,  the  tungstic  acid  contains  silica  and  nndecomposed  silicates. 
In  this  case  wash  residue  into  a  beaker  and  dissolve  out  the  tung- 
stic acid  with  ammonia.     The  ammonium  tungstate  is  filtered  off, 
the  residue  thoroughly  washed,  ignited,  weighed,  and  weight  sub- 
tracted from  that  previously  obtained.     As  a  check  on  this  opera- 
tion, evaporate  the  ammonium  tungstate,  forming  an  acid  salt  in 
lustrous  scales  which  dissolves  with  difficulty.     After  evaporating 
to  dryness,  the  pure  tungstic  acid  is  ignited  and  weighed. 

2.  Berzelius's  method.  —  Fuse    ore  with   double   its  weight   of 
sodium   carbonate,  lixiviate  with   hot  water,  neutralize   the    free 
alkali  so  far  that  the  solution  is  scarcely  acid,  and  add  mercurous 
nitrate  in  excess ;  wash  the  precipitate  formed  with  water  contain- 
ing sodium  chloride,  and,  after  drying,  ignite,  whereby  the  tungstic 
acid  remains  behind  in  a  pure  state.     According  to  Schiebler,1  it  is 
advisable  to  add,  after  precipitation,  a  few  drops  of  ammonia  until 
the  white  precipitate  appears  brownish-black. 

3.  Margueritte's  method. —  The   solution   obtained   after  fusion 
with  soda  is  evaporated  in  water  bath  with  an  excess  of  H2S04, 
the  residue  slightly  heated  to  expel  free  H2S04,  taken  up  with  water 
and  the  alkaline  bisulphate  filtered  off.    The  tungstic  acid  remaining 

i  Ztschft.  f.  Anal.  Chem.  Bd.  1,  p.  71. 


260  ASSAYING. 

upon  the  filter,  is  dried,  detached,  the  filter  incinerated,  and  placed 
together  with  the  tungstic  acid  in  a  small  crucible.  After  moisten- 
ing the  tungstic  acid  with  a  few  drops  of  HN03  and  allowing  the 
latter  to  evaporate,  the  crucible  and  contents  are  heated.  In  heat- 
ing the  acid  readily  acquires  by  deoxidation  a  greenish-blue  color, 
which,  however,  does  not  affect  the  result. 

4.  CobenzVs  method.1 — The  assay  material  previously  bolted 
through  fine  linen  is  placed  in  a  small  flask  and  treated  with  con- 
centrated HN03.  Heated  upon  a  water  bath,  HC1  added  from  time 
to  time  until  disintegration  is  effected.  After  standing  5  or  6  days 
nothing  but  the  yellow  tungstic  acid  can  be  seen.  Now  evaporate 
to  dusty  dryness,  take  up  with  very  dilute  HN03,  evaporate  again, 
and  repeat  these  operations  three  times  or  more.  Finally,  take  up 
with  dilute  HN03  and  some  tartaric  acid  (on  account  of  the  possi- 
ble presence  of  some  antimony).  Heat  to  100°  C.,  filter,  wash  the 
tungstic  acid  together  with  the  undecomposed  silicates  and  silica 
several  times  by  decantation,  and  then  with  hot  water  upon  the 
filter  ;  dissolve  the  tungstic  acid  from  off  the  filter  with  very  dilute 
ammonia,  leaving  the  silica  and  undecomposed  silicates  behind. 
The  ammonium  tungstate  is  then  evaporated  to  dryness  in  a  porce- 
lain crucible,  and  after  heating,  the  straw  yellow  tungstic  acid  is* 
weighed  together  with  the  crucible. 

5.  Separation  of  tungsten  from  tin.' — Metallic  sulphides  and  arse- 
nides are  frequently  associated  with  wolfram.  They  are  generally 
removed  by  digestion  with  aqua  regia.  Tungsten  and  tin  are, 
however,  most  frequently  associated,  and  their  separation  has  often 
to  be  effected. 

According  to  Talbott,  this  separation  is  made  as  follows :  The 
material  containing  the  two  metals  is  intimately  mixed  with  potas- 
sium cyanide,  previously  fused  and  powdered.  The  mixture  is  fused 
in  a  porcelain  crucible,  lixiviated  with  hot  water,  and  the  tungstic 
acid  in  the  potassium  tungstate  formed,  determined  by  one  of  the 
methods  already  given.  In  order  to  neutralize  the  excess  of 
potassium  cyanide,  the  solution  must  be  boiled  with  HN03,  and  the 
tungstic  acid  again  brought  into  solution  by  an  alkali.  Mercurous 
nitrate  is  recommended  for  precipitating  the  tungstic  acid.'2 

1  Monatshefte  fur  Chemie,  etc.     Sitzungsber.  der  Kaiserl.  Akad,  d.     Wis- 
senscliaften  zu  Wien,  April,  1881,  p.  259. 

2  Fortschritte  iin  Probirwesen.     Balling,  Berlin,  1887,  p.  166. 


CHROMIUM — WET   ASSAYS.  261 

B.  Volumetric  assay.  Zettner's  method.1 — Fuse  0.5  to  1.0  gramme 
of  the  finely  powdered  assay  material  with  4  parts  of  sodium  or 
potassium  carbonate,  or  with  3  parts  sodium  carbonate  and  1  part 
saltpetre  in  a  platinum  crucible  over  a  Bunsen  burner.  Lixiviate 
with  hot  water,  filter,  neutralize  the  excess  of  alkali  in  the  heated 
filtrate  with  acetic  acid ;  acidulate  slightly  with  the  same  acid,  then 
heat  to  boiling-,  and  add  a  solution  of  acetate  of  lead  from  a  burette 
until  no  more  precipitate  is  formed.  The  end  of  the  precipitation 
is  indicated  by  the  more  rapid  clearing  of  the  solution.  Now  add  a 
few  drops  more  of  acetate  of  lead,  and  filter  small  portions  of  the 
tungsten  solution  into  test  tubes  near  at  hand  in  order  to  observe 
the  precipitation  more  readily.  Continue  testing  in  this  manner 
until  precipitation  is  complete.  The  number  of  c.c.  of  acetate  of 
lead  multiplied  by  0.0116  gives  the  amount  of  tungstic  acid  in  the 
solution. 

Preparation  of  the  titrating  solution. — Make  a  decimal  lead  solu- 
tion by  dissolving  18.950  grammes  of  extremely  pure  crystallized 
acetate  of  lead,  acidulate  slightly  with  acetic  acid,  and  dilute  to  one 
liter.  The  effective  strength  of  this  solution  is  tested  by  fusing 
11.6  grammes  of  pure,  ignited  tungstic  acid  with  sodium  carbonate, 
taking  up  the  fused  mass  with  water,  acidulating  slightly  with  acetic 
acid,  and  then  determining  the  lead  solution,  which  is  equivalent  to  it. 
If  they  are  not  equal,  they  must  be  made  so  by  repeated  experiment. 


XVII.  CHROMIUM. 

70.    ORES. 

Chrome  iron  ore,  Cr2FeO4,  with  30  to  65  CraO3 ;  crocoisite  (red 
lead  ore),  Pb.CrO4,  with  30.96  CrO3. 

71.    WET  ASSAYS. 

Volumetric  assays  are  less  frequently  made  use  of  than  gravi- 
metric assays,  and  the  latter  vary,  especially  in  the  manner  in 
which  the  very  difficultly  decomposable  chrome  iron-ore  is  decom- 
posed. 

1  Poggendorff,  Anal.  Bd.  130,  p.  16.     Ztschft.  f.  Anal.  Chera.  Bd.  6,  p.  229. 


262  ASSAYING. 

A.   Gravimetric  assays.1 

1.  Direct  assay. — According  to  Pour  eel's  method  :  2  grammes 
of  the  ore  in  coarse  powder  are  highly  heated  in  order  to  facili- 
tate its  comminution.  It  is  then  ground  in  an  agate  mortar,  or 
on  a  porphyry  plate,  to  an  impalpable  powder,  which  should 
show  no  glistening  particles.  This  powder  is  heated  to  120°  C. 
(248°  F.)  until  it  loses  no  more  in  weight,  and  then  a  sample  of 
0.5  gramme  is  quickly  weighed  off.  5  grammes  of  sodium  car- 
bonate are  introduced  into  a  platinun  crucible  and  heated  in  the 
mouth  of  the  muffle  in  order  to  dry  it,  but  not  sufficiently  to  fuse 
it.  The  ore  is  then  intimately  mixed  in  an  agate  mortar,  with 
0.5  gramme  of  saltpetre  and  the  warm  sodium  carbonate  until 
the  mixture  assumes  a  uniform  color.  It  is  then  placed  in  a 
platinum  crucible  and  strongly  heated,  first  at  the  front  of  the 
muffle  and  then  at  the  back,  at  a  white  heat  for  three  hours. 

The  crucible  is  then  taken  out,  wiped  off  after  it  has  become 
cold,  and  placed  in  a  porcelain  dish  containing  0.5  liter  of  distilled 
water  which  completely  impregnates  the  contents  of  the  crucible. 
This  is  allowed  to  stand  for  about  twelve  hours  on  a  sand-bath, 
at  a  temperature  somewhat  less  than  100°  C.  (212°  F.).  It  is 
then  filtered  on  a  very  small  filter,  and  the  crucible  and  dish  are 
washed  out  with  hot  distilled  water.  The  filtrate  containing  the 
potassium  chromate  and  sodium-potassium  aluminate  is  weakly 
acidulated  with  sulphuric  acid,  ammonia  in  excess  is  added,  and 
it  is  then  heated  to  nearly  100°  C.  (212°  F.)  for  at  least  three 
hours.  The  alumina  is  then  filtered  off,  the  filtrate  is  introduced 
into  a  capacious  flask,  hydrochloric  acid  strongly  in  excess  and 
100  cubic  centimeters  of  pure  alcohol  of  40°  are  added,  the  con- 
tents of  the  flask  then  agitated  and  its  neck  closed  by  inserting 
the  neck  of  a  smaller  flask  into  it.  The  liquid  is  now  heated  to 
nearly  100°  C.  (212°  F.)  for  about  forty-eight  hours,  until  the 
reduction  of  chromic  acid  to  chromic  oxide  is  complete  (whereby 

i  Journ  f.  prakt.  Chem.  Ivii.  256  (Calvert).  Fresenius's  Ztschr.  i.  497 
(O'Neill,  Oudesluys,  Genth)  ;  iv.  63  (Souchay)  ;  1861,  p.  34  (Mitscherlich) ; 
1870,  p.  71  (Storer).  Polyt.  Centr.  1856,  p.  701  (Hart).  Dingier,  cxciii.  33 
(Clouet)  ;  cxcvii.  503  (Britton)  ;  ccxxi.  450  (Dittraar)  ;  ccxxiv.  86  (Pels). 
Bullet,  de  la  soc.  de  1'industr.  miner.,  St.  Etieiine,  1878,  livr.  iv.  p.  867 
(Pourcel). 


CHKOMIUM — WET   ASSAYS.  263 

the  liquid  assumes  an  emerald-green  color),  and  the  odor  of 
alcohol  has  disappeared.  Ammonia  in  excess  is  then  added,  the 
liquid  is  allowed  to  stand  for  about  twelve  hours  at  a  tempera- 
ture of  nearly  100°  C.  (212°  F.),  so  that  the  bubbles  are  formed 
on  the  sides  of  the  flask.  The  precipitate  of  hydrated  chromic 
oxide  is  filtered  on  a  small  filter,  washed  with  boiling,  slightly 
ammoniacal  water,  and  dried.  The  chromic  oxide  is  then  ignited 
and  weighed. 

According  to  Fdsy  Calvert's,  Britton's  and  Dittmar's  are  the 
best  methods  for  decomposing  chrome  iron  ores. 

The  following  additional  m-ethods  are  recommended  for  decom- 
posing chrome  iron  ores.  By  Eager. — Mix  the  ore  with  3  parts  of 
sodium  fluoride,  place  in  a  small  graphite  crucible,  cover  with  12 
parts  of  powdered  potassium  bisulphate  and  fuse.  In  five  minutes 
the  charge  should  be  liquid,  and  in  ten  minutes  viscous,  then  disin- 
tegration is  finished.  Fels  recommends  allowing  this  fused  green 
mass,  containing  the  chromium  in  the  form  of  a  fluoride,  to  cool 
and  then  remelt  it  with  the  addition  of  potassium  chlorate.  In 
a  few  minutes  the  mass  becomes  yellow  and  disintegration  is 
complete. 

By  F.  Clarke. — Mix  the  finely  pulverized  ore  with  3  parts  of 
sodium  fluoride  or  cryolite,  covering  with  12  parts  of  potassium 
bisulphate  and  fusing  in  a  covered  platinum  crucible. 

2.  Indirect  assay.1 — The  ore  is  fused  with  potassium  nitrate 
and  sodium  carbonate  (in  the  same  manner  as  arsenic,  p.  252), 
the  alkaline  chromates  are  lixiviated.  The  solution  is  saturated 
with  acetic  acid,  and  boiled,  in  order  to  remove  the  carbonic  acid. 
It  is  then  diluted  with  water  (to  prevent  a  separation  of  silver 
acetate),  and  a  sufficient  quantity  of  silver  nitrate  is  added.  The 
precipitate  of  silver  chromate  will  then  contain  to  one  atom  of 
chromium,  one-half  atom  of  silver  (100  Ag=  48.69  Cr  =  70.92- 
Cr2O3=  93.15  CrO3).  The  precipitate,  together  with  the  filter,  is 
boiled  in  strongly  diluted  hydrochloric  acid,  the  silver  chloride 
formed  is  filtered  off,  smelted  with  lead,  and  cupelled,  and  the 
chromium  calculated  from  the  resulting  quantity  of  silver. 

B.   Volumetric  assay. — 1  gramme  of  the  ore  is  powdered  and 

1  Piattner-Richner's  Lothrohrprobirkunst,  1878,  p.  651. 


264  ASSAYING. 

ground  as  fine  as  possible.  It  is  then  fused  with  soda  and 
saltpetre  and  converted  into  alkaline  chromate  (p.  262).  It  is 
then  supersaturated  with  sulphuric  acid  and  a  weighed  quantity 
of  pure  ferrous  sulphate  or  ammonio-ferrous  sulphate,  when, 
the  ferrous  oxide  becoming  oxidized  at  the  cost  of  the  chromic 
acid,  the  latter  is  transformed  into  chromic  oxide,  and  the 
color  of  the  reddish-yellow  solution  becomes  distinctly  green 
(2CrO3  +  6FeSO4  4-  6SO3  =  Cr2S3O12  -f-  3Fe2S3O12) ;  therefore,  6 
equivalents  of  FeO  correspond  to  2  equivalents  CrO3=3  :  1. 
The  residue  of  ferrous  oxide  which  has  not  been  decomposed  is 
titrated  with  solution  of  potassium  permanganate,  when  the  final 
reaction  will  be  more  distinct  the  stronger  the  liquid  has  been 
acidulated  with  sulphuric  acid,  which  causes  the  green  color  of 
the  chromic  oxide  to  become  pale. 

XVIII,  MANGANESE, 

72.    ORES. 

Pyrolwdte,  MnO2,  with  62.8  Mn  and  37.2  O ;  braunite,  Mn2O3, 
with  69.23  Mn  and  30.77  O;  haurniannite,  Mn3O4,  with  71.7 
Mn  and  28.3  O;  manganite,  Mn2O3  +  H2O,  with  89.9  Mn2O3 
and  10.1  H2O ;  varvicite,  (Mn2O3  -4-  H2O)  -f  2MnO2,  with  14.23 
MuO,  80.79  O,  and  4.98  H2O;  psilomelane,  (Mn.Ba.K2.Li2)  O-f 
4  MnO2,  with  20  to  60  MnO2;  wad,  MnO.2Mn2O3  +  3H2O. 

73.    ASSAYS   OF   PYROLUSITE.1 

The  percentage  of  manganese  in  an  ore,  which  is  of  interest  to 
the  iron  manufacturer,  is  generally  determined  by  chemical 
analysis  (Tamm2  has  given  a  process  of  preparing  manganese 
carbide,  from  pyrolusite),  while  the  value  of  an  ore  for  other 
technical  purposes  (manufacture  of  chlorine  and  of  chloride  of 
ime,  the  preparation  of  oxygen)  is  judged — 

1 .  By  the  quantity  of  chlorine  which  the  ore  yields  on  treatment 

1  Muspratt's  Chemie,  iv.  1111. 

2  Dingier,  ccvi.  136.     B.  u.  h.  Ztg.  1873,  p.  55. 


MANGANESE — ASSAYS  OF  PYROLUSITE.  265 

with  hydrochloric  acid  (MnO2-f  4C1H=  MnCla+  2H2O-hCl2= 
81.2  per  cent.  Cl),  or,  with  common  salt  and  sulphuric  acid 
(Mn02  -h  2NaCl  +  2H2SO4  -  MnSO4-f  Na2SO4  -f  2H2O  4-  2C1  = 

81.2  per  cent.). 

If  an  ore  contains  ferrous  oxide,  for  instance  in  the  form  of 
spathic  or  magnetic  iron,  a  part  of  the  chlorine  evolved  from  the 
hydrochloric  acid  is  consumed  in  the  higher  oxidation  of  the 
ferrous  oxide,  and  is  therefore  lost  for  technical  use.  Only  so 
much  of  the  chlorine  as  is  actually  obtained  from  pyrolusite  is 
of  value  to  the  buyer,  and  the  assays  which  give  this  (for  in- 
stance, Bunsen's  and  Gay-Lussac's)  are  to  be  preferred  to  those 
which  give  the  total  amount  of  chlorine  without  taking  into  con- 
sideration that,  when  ferrous  oxide  is  present,  the  chlorine  is  not 
all  available  for  practical  purposes. 

2.  By  the  quantity  of  oxygen  the  pyrolusite  yields  when  ignited 
or  treated  with  sulphuric  acid  (MnO2  4-  SO3  =  MnSO4  +  O  = 

18.3  per  cent.). 

3.  By  the  foreign  admixtures  according  to  their  quality  and 
quantity.     Substances  soluble  in  acids  (for  instance,  calcium  and 
iron  carbonates)  are  especially  injurious.     They  increase  unne- 
cessarily the  cost  of  manufacturing  chlorine,  and,  by  evolving 
considerable  quantities  of  carbonic  acid,  exert  a  disturbing  in- 
fluence on  the  preparation  of  chloride  of  lime.     For  this  reason, 
the  quantity  allowed  is  sometimes  limited  by  contract  to  one  per 
cent. 

The  quantity  of  acid  required  for  the  decomposition  is  de- 
termined by  finding  the  quantity  of  pure  marble  dissolved  by  a 
given  quantity  of  hydrochloric  acid ;  then  allowing  the  same 
quantity  of  acid  to  act  on  a  known  quantity  of  the  ore ;  then  when 
chlorine  ceases  to  be  evolved,  introducing  the  marble,  and  when 
the  evolution  of  carbonic  acid  has  ceased,  removing  the  marble 
and  weighing.  The  quantity  of  acid  is  ascertained  from  the 
difference  in  the  loss  of  marble  in  the  two  cases.  100  parts  of 
marble  saturate  70.5  parts  of  dry  and  205  parts  of  aqueous  hy- 
drochloric acid  of  1.17  specific  gravity  ;  and  when  the  acid  is  of 
1.09  specific  gravity,  corresponding  to  18.2  per  cent,  of  dry  acid, 
7.3  milligrammes  of  dry  acid  correspond  to  1  gramme  of  dis- 
solved marble. 


266  ASSAYING. 

4.  By  the  decomposability  and  the  physical  condition  of  the  ore, 
as  they  require  different  quantities  of  acid,  for  instance,  Spanish 
ore  more  than  Nassau  ore. 

Hydrochloric  acid  dissolves  the  ferrous  oxide  contained  in  man- 
ganese ores  more  readily  than  sulphuric  acid,  and  differences  may, 
therefore,  arise  in  the  yield  of  available  chlorine  from  an  ore, 
according  as  one  or  the  other  acid  has  been  used,  since  the  more 
ferrous  oxide  dissolved,  the  more  chlorine  is  kept  back  (p.  265). 

5.  By  the  constitution  of  the  ore,  which  requires  also  different 
quantities  of  acid. 

1  atom  pyrolusite  requires  4  atoms  hydrochloric  acid  to  yield 
2  atoms  of  chlorine  (MnO2  +  4C1H  .  MnCl2  +  Clt  +  2H2O)  • 
while  braunite  requires  6  atoms  of  the  acid  (Mn2O3  +  6C1H  = 
2MnCl2+Cl2  +  3H20). 

6.  By  the  amount  of  hygroscopic  water,  which  is  sometimes  con- 
siderable, and  must  be  removed  by  drying,  for  instance,  upon 
Fresenius's  disk  (Fig.  2,  p.  25),  at  100°  or  110°  to  115°  C.  (212° 
or  230°  to  239°  F.). 

It  is  customary  to  represent  the  commercial  value  of  manganese 
ores,  whether  the  available  chlorine  or  oxygen  is  to  be  ascer- 
tained, in  terms  of  manganese  peroxide  equivalent  to  the  chlorine 
or  oxygen  yielded  (even  if  the  ore  does  not  contain  it,  as,  for  in- 
stance, braunite) ;  namely,  2  atoms  of  chlorine  (17),  or  1  atom 
oxygen  (16)  =  1  atom  peroxide.  Frequently  60  per  cent,  of 
peroxide  is  taken  as  the  standard  in  commerce,  and  from  a  fixed 
price  for  this,  the  value  of  the  ore  is  determined  according  to  the 
higher  or  lower  percentage  of  peroxide  it  contains. 

The  following  Table  gives  the  theoretical  yield  of  oxygen, 
chlorine,  and  peroxide  of  the  different  ores  : — 

Oxygen  Chlorine  Peroxide 

per  cent.  per  cent.  per  cent. 

Pyrolusite    ....       18                81.2  100 

Braunite       .         .         .         .10                45.1  55.5 

Hausmannite        .        <•       »        6.8             30.6  37.7 

Manganite    .         .         ;         .         9                45.6  50. 

Varvicite     ..  .•    ...     .'      .      13.8             62.2  76.6 

A.  Gravimetric  assays. — These  require  but  simple  utensils, 
and  can  be  easily  executed  by  not  very  experienced  operators, 


MANGANESE — ASSAYS   OF  PYROLTJSITE. 


267 


but  the  results,  if  certain  substances  are  present,  are  inaccurate, 
or  require  check  assays. 

1.  Method  of  Fresenms-WilL* — 2  to  5  grammes  of  very  finely 
powdered  ore  are  weighed  out  and  placed  in  the  flask  A  (Fig. 
79),  made  of  thin  glass,  and  capable  of  holding  about  120  cubic 
centimeters.  To  this  are  added  two  and  a  half  times  the  quantity 
of  powdered  neutral  potassium  oxalate  (5  to  12.5  grammes),  and 
the  flask  is  then  filled  to  about  one-third  with  water.  The  flask 


Fig.  79. 


Fig.  80. 


A  is  hermetically  connected  by  the  tube  c  (corks  saturated  with 
wax  or  paraffine,  or  caoutchouc  stoppers  should  be  used)  with  the 
flask  B  half  filled  with  English  sulphuric  acid.  The  tube  a  is 
closed  with  a  plug  of  wax,  or  a  caoutchouc  tube  with  a  glass  rod, 
and  the  whole  apparatus  is  weighed.  The  air  is  then  aspirated 
at  6,  in  order  to  create  a  partial  vacuum  in  the  flask  B,  by  which 
the  air  above  the  liquid  in  flask  A  will  likewise  be  somewhat 
rarefied,  in  consequence  of  which  the  acid  from  B  will  pass  through 
c  into  A,  after  the  suction  ceases.  Carbonic  acid  is  developed  by 
the  action  of  the  sulphuric  acid  upon  the  ore  and  oxalate  (MnO, 
+  C2O3  +  SO3  =  MnSO4  +  2CO2),  which  passes  through  c  into 
B,  is  dried  in  passing  through  the  sulphuric  acid,  and  escapes 
through  6.  The  drawing  over  of  acid  by  suction  is  repeated 

1  Ann.  der  Chemie  u.  Pharra.  xlix.  137.     Fresenius's  Ztschr.  i.  48  (Rohr)  ; 
i.  110  Kolbe)  ;  i.  81,  110  (Kolbe).     Dingier,  clxxxvi.  210  (Lunge). 


268  ASSAYING. 

until  no  more  carbonic  acid  is  developed,  and  no  black  residuum 
is  observed  in  A,  gentle  heating  being  employed  towards  the 
last,  the  plug  or  stopper  is  now  removed  from  «,  suction  is  ap- 
plied at  6,  in  order  to  remove  the  carbonic  acid  contained  in  the 
apparatus.  When  this  is  entirely  cold  the  apparatus  is  weighed, 
and  the  percentage  of  peroxide  calculated  from  the  loss  of  car- 
bonic acid;  2  atoms  CO2  (88)  being  equal  to  1  atom  MnO2  (87.14, 
or,  in  round  numbers,  87). 

If  carbonates  are  present,  the  result  will  be  affected,  and  the 
following  process  becomes  necessary  to  neutralize  their  influence. 
A  little  sulphuric  acid  is  drawn  over  from  the  flask  B  into  A, 
the  latter  containing  only  ore  and  water.  The  carbonic  acid 
evolved  is  removed  by  aspiration,  and  the  apparatus  is  weighed, 
the  required  quantity  of  potassium  oxalate  being  weighed  along 
with  the  apparatus  upon  the  same  scale  pan.  The  oxalate  is  then 
quickly  poured  into  the  flask  J.,  and  the  further  operation  con- 
ducted as  above. — According  to  Mokr,  a  percentage  of  ferrous 
oxide1  in  the  ore  (for  instance,  magnetic  and  spathic  iron)  does 
not  affect  the  result  of  the  assay,  but  gives  too  high  a  percentage 
of  chlorine  for  commercial  purposes,  since  a  part  of  the  chlorine 
is  consumed  in  the  higher  oxidation  of  the  iron. — Lighter  appa- 
ratus than  that  of  Will  and  Fresenius  is  described  by  Mohr,  Kolbe, 
and  Rose  (Fig.  80) ;  A,  flask  for  the  reception  of  the  ore,  potas- 
sium oxalate,  and  water ;  (7,  glass  tube  for  sulphuric  acid,  diluted 
with  an  equal  volume  of  water;  B,  drying-tube  with  calcium 
chloride,  supported  at  h.  The  apparatus  is  weighed,  and  then 
tilted  in  order  to  transfer  acid  from  C  through  the  tube  c  to  A 
(or  by  aspirating  on  the  calcium  chloride  tube  at  /).  The  carbonic 
acid  developed  is  allowed  to  escape  through  the  drying^tube  B,  and 
finally  the  carbonic  acid  is  expelled  from  the  apparatus  by  suc- 
tion at  I'. 

2.  Method  of  Fikentscher-Nolte.2 — 1  to  5  grammes  of  ore,  8 
times  the  quantity  of  ferrous  sulphate  free  from  ferric  oxide,  an 

1  Fresenius's  Ztschr.  1869,  p.  314  CMolir)  ;  1871,  p.  310  (Luck)  ;  Dingier, 
cxcvii.  422  (Pattinson).     B.  u.  h.  Ztg.  1871,  p.  312  (Sherer). 

2  Journ.  f.  prakt.  Chern.  xviii.  160,  173  (Fikentscher).     B.  u.  h.  Ztg.  1859, 
p.  149;  1864,  p.  374  (Nolte). 


MANGANESE — ASSAYS   OF   PYBOLUSITE.  269 

accurately  weighed  strip  of  bright  sheet-copper  4  to  5  times  the 
weight  of  the  ore,  30  to  35  cubic  centimeters  of  hydrochloric  acid 
of  1.12  specific  gravity,  and  distilled  water  are  placed  in  a  suita- 
ble flask  provided  with  a  rubber  valve  (Fig.  11,  p.  36).  The 
contents  are  kept  at  a  boiling  heat  (at  least  two  hours)  until  the 
solution,  at  first  brown,  becomes  nearly  colorless,  when  the  ferric 
chloride,  which  was  first  formed,  is  reduced  to  ferrous  chloride  by 
the  copper,  the  weight  of  which  correspondingly  decreases  (MnO2 
+  2FeCl24-2HCl  =  MnCl2  +  Fe2Cl6+2H20;  then,  Fe2Cl6+2Cu 
=  2FeCl2  +  Cu2Cl2).  The  flask  is  then  quickly  filled  with  boil- 
ing water  free  from  air.  The  liquid  is  then  poured  oif,  the  strip 
of  copper  quickly  thrown  into  water,  rinsed,  and  dried  with  ab- 
sorbent paper,  but  without  rubbing  it ;  then  completely  dried  at 
100°  C.  (212°  F.),  allowed  to  become  cold  in  the  desiccator,  and 
then  weighed.  The  percentage  of  manganese  peroxide  is  calcu- 
lated from  the  loss  of  copper,  as,  according  to  the  above  equation, 
2  atoms  of  dissolved  copper  (126.8)  correspond  to  1  atom  of  per- 
oxide (87.14). 

The  oxidizing  action  of  the  air  upon  copper  must  be  avoided,  as 
otherwise  more  would  be  dissolved  than  the  required  quantity. 
For  this  reason  a  flask  provided  with  a  rubber-valve  should  be 
used,  ferrous  sulphate  free  from  ferric  oxide.  The  copper  should 
further  be  kept  constantly  covered  by  the  hydrochloric  acid, 
thoroughly  boiled  water  used,  and  the  copper  quickly  rinsed  off. 
In  case  the  ore  contains  ferric  oxide,  a  check  assay  must  be 
made,  as  it  forms  ferric  chloride  with  hydrochloric  acid,  and  this 
contributes  to  the  solution  of  the  copper.  This  must  be  calcu- 
lated for  by  treating  a  quantity  of  ore  equal  to  that  of  the  prin- 
cipal assay,  with  hydrochloric  acid,  but  first  without  copper.  This 
is  now  heated  until  all  the  chlorine  has  been  expelled,  the  weighed 
copper  is  now  added,  and  the  liquid  boiled  until  it  becomes  color- 
less. The  loss  in  weight  of  copper  by  ferric  chloride  alone  is 
now  determined,  and  this  is  deducted  from  the  loss  which  takes 
place  in  the  principal  assay. 

E.  Volumetric  assays. — Those  methods  which  give  only  the 
actually  available  chlorine,  as  Bunsen's  and  Gay-Lussac's,  de- 
serve the  preference,  as  other  methods  indicate  too  large  a  per- 


270  ASSAYING. 

centage  of  chlorine,  which,  in  operations  on  the  large  scale  where 
the  ore  contains  ferrous  oxide,  cannot  be  depended  on. 

Perry1  found  that  an  ore  which  gave  100  MnO2  according  to 
Fresenius's  method  yielded  99.1  according  to  Mohr's,  100.6  ac- 
cording to  Hempel's,  97.8  according  to  Gay-Lussac's,  and  98.4 
per  cent.  MnO2  according  to  Bunsen's.  The  differences  are  partly 
explained  by  the  fact  that,  in  making  the  assays,  the  action  of  the 
ferrous  oxide  present  is  taken  into  consideration  in  some,  while 
in  others  it  is  not ;  and  that,  when  sulphuric  acid  is  used  (Fresen- 
ius,  Hempel*),  or  hydrochloric  acid  (Bunsen,  Gay-Lussac\  more 
or  less  ferrous  oxide  is  dissolved,  as  it  is  not  equally  soluble  in 
these  acids. 

1.  Bunsen' s  method  with  iodine? — This  is  based  upon  the  prin- 
ciple that,  when  chlorine  evolved  from  manganese  ore  by  hydro- 
chloric acid  (MnO2  +  4ClH=MnCl2  +  2Cl4-2H2O)  is  introduced 
into  a  solution  of  potassium  iodide,  it  separates  from  this  a  cor- 
responding quantity  of  iodine,  indicated  by  the  appearance  of  a 
brown  color.  After  the  addition  of  starch,  which  colors  the  solu- 
tion blue,  the  quantity  of  separated  iodine  is  determined  by 
titrated  solution  of  sodium  hyposulphite,  which  is  added  until  the 
color  has  disappeared  (2Na2S2O3-t-2I  =  Na2S4Ort+2NaI);  whence 
2  atoms  of  chlorine  correspond  to  2  atoms  of  iodine,  and  these  to 
1  atom  of  manganese  peroxide.  This  assay  is  very  accurate,  and 
the  results  obtained  are  not  affected  by  any  admixtures,  but  it 
requires  somewhat  skilful  manipulation. 

The  retort  d  (Fig.  81),  the  neck  of  which  is  provided  with 
two  bulbs  in  order  to  lessen  the  danger  of  loss  by  overflow,  is 
filled  one-third  full  with  a  freshly  prepared  solution  of  one  part 
potassium  iodide  in  ten  parts  of  water.  The  potassium  iodide 
must  not  become  colored  on  the  addition  of  acid,  as  this  would 
indicate  the  presence  of  potassium  iodate,  from  which  more  iodine 
would  be  separated  by  chlorine.  The  retort  is  then  inverted  (see 
Fig.  81),  and  a  glass  tube  provided  with  a  bulb  c  is  introduced 

1  Dingier,  ccxxvi.  194. 

2  Mohr,  Titrirmethode,  1874,  p.  625.     Muspratt's  Chemie,  iv.  1118.     Fre- 
senius's  Ztschr.  1869,  p.  314;  1870,  p.  410.     Journ.   f.  prakt.  Chem.,  Neue 
Folge,  xviii.  101  (Marawski  und  Stingl). 


MANGANESE — ASSAYS   OF   PYROLUSITE. 


271 


into  the  neck  of  the  retort.  The  other  somewhat  wider  end  of 
the  glass  tube  is  furnished  with  a  caoutchouc  tube  6,  previously 
boiled  in  a  solution  of  potassium  hydrate.  0.1  to  0.5  gramme  of 
very  finely  powdered  ore  is  poured  into  the  flask  a.  This  is  then 

Fig.  81. 


about  two-thirds  filled  with  fuming  hydrochloric  acid,  the  neck 
of  the  flask  is  quickly  pushed  into  the  moistened  caoutchouc  tube 
6,  so  that  glass  touches  glass.  The  flask  is  now  slowly  heated 
over  a  spirit-lamp,  so  as  to  avoid  the  passage  of  liquid  from  d 
back  into  a.  The  heating  is  continued  until  the  greenish*  color 
of  the  chlorine  in  the  bulb  of  the  connecting  tube  disappears,  the 
ore  is  entirely  decomposed,  and  a  peculiar  crackling  noise  is 
heard  in  the  flask.  The  heat  is  somewhat  increased  for  about 
half  a  minute  after  the  crackling  noise  has  been  perceived,  to 
prevent  the  liquid,  containing  about  5  grammes  of  solid  potassium 
iodide  and  colored  brown  ]by  the  separated  iodine,  from  passing 
over  into  the  flask.  The  gas-conducting  tube  c  is  then  with- 
drawn from  the  retort  with  the  left  hand,  the  heating  of  the  flask 
a  being  continued  all  the  while  by  holding  the  spirit-lamp  below 
it  with  the  right  hand  (if  these  manipulations  are  not  conducted 
with  proper  skill,  there  is  danger  that  the  liquid  in  the  retort  will 
pass  over).  The  tube  is  then  washed  off  in  a  beaker-glass.  The 
retort,  containing  the  brown  iodine  solution,  is  corked,  and  care- 
fully shaken,  so  that  the  solution  may  take  up  all  the  free  iodine, 
during  which  operation  the  liquid  must  not  come  in  contact  with 
the  cork.  After  the  fluid  has  become  entirely  cold,  it  is  poured 
out  in  the  beaker-glass.  Should  the  liquid  contain  any  undis- 
solved  iodine,  a  few  crystals  of  potassium  iodide  must  be  added 


272 


ASSAYING. 


before  the  contents  of  the  retort  are  emptied  into  the  beaker-glass. 
It  is  then  diluted  to  the  bulk  of  one-half  liter.  100  cubic  centi- 
meters of  this  are  taken,  introduced  into  a  separate  vessel,  and 
titrated  sodium  hyposulphite,  which  is  added  to  it  as  long  as  a  red 
color  is  still  distinctly  perceptible.  About  2  grammes  of  starch 
liquor  are  added,  and  then  more  sodium  hyposulphite,  drop  by 
drop,  until  the  blue  color  which  has  been  formed  just  commences 
to  disappear.  If  necessary,  the  assay  may  be  controlled  by  titrat- 
ing back  with  a  normal  solution  of  iodine,  until  the  blue  color 
appears  again.  The  standard  solution  of  sodium  hyposulphite  is 
prepared  by  dissolving  24.8  grammes  of  sodium  hyposulphite  in 
water,  and  diluting  the  solution  to  1  liter.  0.1  to  0.2  gramme  of 
pure  iodine  is  then  dissolved  in  18  grammes  of  potassium  iodide, 

free  from  iodic  acid,  and  this 
solution  is  also  diluted  to  1 
liter,  when  1  cubic  centimeter 
of  normal  solution  of  sodium 
hyposulphite  will  correspond 
to  0.0127  gramme  of  iodine 
contained  in  1  cubic  centi- 
meter of  solution,  so  that  equal 
volumes  correspond. 

Fig.  82  represents  a  modi- 
fied form  of  this  apparatus,  in 
which  the  bulbed-tube  at- 
tached to  the  dissolving  flask 
passes  into  a  long  and  narrow 
tube,  which  is  cooled  by  im- 
mersion in  cold  water,  and 
contains  a  higher  column  of 
potassium  iodide  solution. 

2.  LevoVs  method  with  iron.1 
— 0.5  to  0.6  gramme  of  man- 
ganese ore,  and  0.8  to  1  gramme 

of  piano  wire  (containing  on  an  average  99.6  per  cent,  of  pure  iron), 
are  treated  with  exclusion  of  air  with  hydrochloric  acid,  in  a  flask 


1  Dingier,  Ixxxv.  299  (Level)  ;  cxcvii.  422  (Pattinson).   Fresenius's  Ztschr. 
1869,  p.  509  (Teschemacher  u.  Smith). 


MANGANESE — ASSAYS  OF  PYROLUSITE.  273 

provided  with  a  rubber  valve  (Fig.  11,  p.  36)  ;  when,  from  the 
resulting  ferrous  chloride,  a  quantity  of  ferric  chloride  corre- 
sponding to  the  chlorine  developed  will  be  formed  (MnO2  4- 
4HC1  =  MnCl2  -f  2C1  +  2H2O  and  2C1  +  2FeCl2  =  Fe2Cl4). 
The  liquid  is  diluted  to  0.5  liter.  100  cubic  centimeters  of  this 
are  taken,  and,  after  having  become  entirely  cold,  the  non- 
oxidized  quantity  of  ferrous  oxide  is  determined  by  titration  with 
potassium  permanganate  (p.  123).  The  quantity  of  iron  oxidized 
by  the  chlorine  is  determined  from  the  difference ;  and  2  atoms 
of  iron  (112)  correspond  to  1  atom  of  manganese  peroxide 
(87.14). 

Ammonio-ferrous  sulphate,  FeSo4  +  (NH4)2SO4  +  6H2O,  may  be 
used  instead  of  metallic  iron,  in  the  proportion  of  about  7 
grammes  to  1  gramme  of  manganese  ore  with  70  per  cent,  of 
peroxide,  and  8  to  9  grammes  if  the  percentage  is  higher ;  when 
2  atoms  of  the  salt  (784)  correspond  to  1  atom  of  manganese 
peroxide  (87.14).  The  assay  solution  to  be  titrated  should  be 
cold,  and  strongly  diluted,  to  prevent  the  hydrochloric  acid  from 
being  decomposed  by  the  potassium  permanganate ;  or,  potassium 
bichromate1  may  be  used  instead  of  potassium  permanganate.  In 
this  assay  (iron  test),  which  is  much  used  in  England,  a  part  of 
the  chlorine  is  consumed  for  the  higher  oxidation  of  the  ferrous 
oxide,  if  any  be  contained  in  the  ore. 

Volhard's  method.2 — This' method  is  based  upon  the  fact  that  only 
in  the  presence  of  salts  of  calcium,  magnesium,  barium,  and  tin 
monoxide,  manganese  is  completely  precipitated  as  dioxide  by 
potassium  permanganate. 

3MnO  +  Mn207  =  5Mn02. 

In  the  absence  of  these  salts  a  combination  of  dioxide  with  varying 
quantities  of  monoxide  is  precipitated,  and  consequently  a  portion  of 
the  manganese  is  withdrawn  from  the  titering  solution.  Heat  and 
concentration  aid  in  the  formation  and  separation  of  the  dioxide, 
while  the  addition  of  an  acid  retards  the  reaction  ;  HC1  and  H2S04 
should  therefore  not  be  present.  A  drop  of  HN03,  however,  added 

1  Mohr,  Titrirmethode,  1874,  p.  632.     Polyt.  Centrbl.  1871,  p.  1117  ;  Oxal- 
saureprobe  in  Fresenius's  Ztschr.  1870,  p.  410. 

2  Annal.  d.  Chem.  t.  198,  p.  318.     Dingler's  Journ.  Bd.  235,  p.  387.    Bg.  u. 
Httumsch.  Ztg.  1880,  p.  150.   Oesterr.  Ztschft.  f.  Bg.  u.  Httnwsn.  1880,  p.  168. 

18 


274  ASSAYING. 

before  the  beginning  of  the  titration,  facilitates  the  precipitation  of 
Mn02  in  case  there  is  a  small  amount  of  organic  matter  present, 
which  has  the  effect  of  producing  a  turbidity  which  renders  the 
determination  difficult ;  while  small  portions  of  ferric  oxysalts  exert 
no  disturbing  influence  in  the  acidulated  solution,  they  prevent  pre- 
cipitation in  a  neutral  solution  and  render  it  difficult  to  recognize 
the  color  of  the  solution.  The  ferric  salts  are  removed  by  adding 
pure  zinc  oxide,  whereby  all  the  ferric  oxide  is  precipitated  as  zinc 
oxide  containing  hydroxide. 

The  assay  is  executed  as  follows. — Dissolve  2  grammes  of  the 
finely  powdered  ore  in  a  mixture  of  3  parts  H2S04  (1.13  sp.  gr.)  and 
1  part  HN03  (1.4  sp.  gr.)  and  evaporate  to  dryness.  Digest  the 
residue  with  HN03,  dilute  with  water  and  rinse  the  solution  into  a 
half  liter  flask,  neutralize  excess  of  acid  with  caustic  soda  and  pre- 
cipitate the  ferric  oxide  with  pure  oxide  of  zinc,  adding  the  latter 
while  shaking  until  the  supernatant  liquid  assumes  a  milky  tur- 
bidity :  when  the  precipitation  is  complete,  dilute  up  to  mark,  and 
after  allowing  to  settle,  filter.  Place  100  c.c.  of  the  filtrate  in  a 
boiling  flask,  add  one  drop  of  HN03,  heat  nearly  to  boiling  and 
titrate  with  permanganate  solution  until  the  fluid  assumes  a  pale- 
red  color. 

Determining  the  strength  of  the  permanganate.  —  Yolhard1  re- 
commends the  following  method.  Dilute  10  c.c.  of  a  5  per  cent, 
solution  of  potassium  iodide  with  150  to  200  c.c.  of  water,  add  4  or 
5  drops  of  HC1  and  run  in,  with  constant  stirring,  20  c.c.  of  per- 
manganate. The  liberated  iodine  is  titrated  with  sodium  hyposul- 
phite ;  this  sodium  salt  is  measured  for  comparison  with  potassium 
bichromate,  which  also  separates  iodine  in  acid  solutions  of  potassium 
iodide. 

Hampers  method.2 — 1.  Decompose  one  gramme  of  the  assay 
material  with  20  c.c.  of  HNO,  (1.2  sp.  gr.).  From  this  concentrated 
solution,  containing  free  acid,  precipitate  the  manganese  as  dioxide 
by  potassium  chlorate  or  bromate  by  adding,  in  two  or  three 
portions,  8  to  10  grammes  of  one  of  these  salts  in  the  solid  state. 
Boil  solution  for  1^  hours,  dilute  with  hot  water,  filter  through 
asbestus  and  place  the  precipitate  with  the  asbestus  and  a  few 
grains  of  sodium  bicarbonate  into  the  same  flask  in  which  the  solu- 
tion and  precipitation  were  made.  Now  add  dilute  H2S04  and  a 

•  i  Ztschft.  f.  Anal.  Chem.  Bd.  20,  p.  274. 
2  Chemikerztg,  1883,  p.  1106.     Bg.  u.  Httnmsch.  Ztg.  1883,  p.  537. 


MANGANESE — ASSAYS  OF   PYROLUSITE.  275 

measured  quantity  of  ammonium  ferric  sulphate  solution,  and  after 
closing  flask  with  cork  and  rubber  valve,  heat  in  sand  bath  until  the 
dark-brown  precipitate  disappears.  Allow  to  cool  and  titer  back  the 
excess  of  ferric  sulphate  with  permanganate.  ...  It  is  best  to  use 
for  the  titrating  solution  14.2817  grammes  of  double  iron  salt  and 
1.15095  grammes  of  permanganate,  each  dissolved  in  one  liter  of 
water.  Both  solutions  are  equivalent,  and  1  c.c.  of  either  corre- 
sponds to  0.001  gramme  of  manganese. 

2.  Heat  0.25  to  1.0  gramme  of  ferro-manganese  in  a  covered  por- 
celain dish  with  20  c.c  of  HN03  (sp.  gr.  1.12).  Add  2  grammes  of 
solid  ammonium  nitrate,  evaporate  to  dryness,  heat  strongly  until 
no  more  vapors  escape,  in  order  to  decompose  the  nitrates,  and  add 
20  to  40  c.c.  of  phosphoric  acid  of  1.7  sp.  gr.  Stir  with  a  glass  rod, 
cover  dish,  and  heat  in  an  air  bath  to  140°  C.  In  from  6  to  10 
hours  beautiful  violet  manganese  phosphate  and  colorless  ferric 
phosphate  are  formed.  The  titrating  solutions  used  in  this  deter- 
mination are  made  only  one-half  the  strength  of  those  used  in  the 
previous  method.  The  reaction  is  as  follows :  Mn203  +  2FeO  = 
2MnO  +  Fe203.  In  the  previous  method  it  is  Mn02  -f  2FeO  = 
MnO  +  Fe2O3. 

BelanVs  method.1 — Dissolve  0.5  to  2.0  grammes  of  the  ore  in  ^ 
liter  Erlenmeyer  flask  with  25  to  40  c.c.  of  HC1(1.19  sp.gr.) ;  if  ferrous 
oxide  or  manganous  oxide  be  present  in  the  ore,  the  solution  is  again 
boiled  with  10  c.c.  of  HN03  (1.4  sp.  gr.)  for  each  gramme  of  ore. 
Rinse  solution  and  residue  into  a  graduated  liter  flask  and  neutralize 
with  zinc  oxide.  The  rest  of  the  method  is  the  same  as  Yolhard's. 
With  a  very  small  content  of  iron  the  solution  is  turbid,  but  with  a 
considerable  quantity  precipitation  takes  place  suddenly.  An  excess 
of  zinc  oxide  is  not  injurious.  When  the  precipitation  is  finished 
the  flask  is  filled  up  to  the  liter  mark,  and,  after  filtering  off,  250  c.c. 
of  the  filtrate  are  taken  for  titration. 

C.  Electrolytic  assays. — Manganese  is  one  of  the  metals  which  are 
oxidized  by  the  current  to  the  peroxide,  which  separates  at  the  posi- 
tive electrode.  The  separation  of  the  dioxide  is  complete  from  a 
solution  of  potassium  manganese  oxalate  (it  is  not  complete  from  a 
solution  of  the  ammonium  double  salt),  and  also  from  solutions  con- 
taining free  HNO3  or  H.2S04.  By  the  former  method  the  solution 
of  manganese  salt  is  treated  with  a  slight  excess  of  potassium 
oxalate,  diluted  and  precipitated  with  a  current  of  9  to  12  c.c.  of 

i  Stahl  und  Eisen,  1886,  p.  152. 


276  ASSAYING. 

oxyhydrogen  gas  per  minute.  If  the  quantity  is  small,  the  dioxide 
adheres  to  the  positive  electrode  firmly  enough  to  be  converted,  after 
washing,  into  mangano-manganic  oxide  by  ignition  of  the  previously 
weighed  electrode.  With  larger  quantities  it  is  best  to  make  the 
platinum  dish  the  positive  electrode,  and  when  the  reaction  is  ended 
to  endeavor  to  convert  the  dioxide  into  mangano-manganic  oxide 
by  ignition  without  filtration.  If  this  is  impossible,  the  precipitate 
is  filtered  off,  washed  with  hot  water,  and  converted  into  either 
mangano-manganic  oxide  or  sulphate.  As  ammonium  sulphide  is 
unsuited  to  show  the  end  of  the  reaction,  owing  to  the  formation 
of  oxalic  acid,  which  hinders  the  precipitation  of  the  sulphide,  the 
best  test  is  to  evaporate  a  small  portion  of  the  solution  in  platinum 
foil,  and  fuse  with  sodium  carbonate.1 

According  to  Luckow,2  in  order  to  make  the  dioxide  adhere 
firmly  to  the  positive  electrode,  the  solution  must  be  neutral  or 
only  very  slightly  acid,  and  the  current  not  too  strong.  In  very 
dilute  solutions  acidulated  with  much  HN03  or  a  mixture  of  HNO3 
and  H^S04  permanganic  acid  is  formed,  which  is  readily  recognized 
by  its  red  color.  The  presence  of  organic  acids  as  well  as  ferrous 
oxide,  chromic  oxide,  or  of  ammoniacal  salts  prevents,  according  to 
Schucht,3  the  formation  of  permanganic  acid. 

In  the  separation  of  manganese  as  dioxide,  from  an  acid  solution, 
it  is  better  to  use  a  few  drops  of  H2S04  instead  of  HN03,  as  the 
latter  is  converted  by  the  current  into  ammonia,  which  may  precipi- 
tate some  of  the  other  metals  present.  Manganese  may  be  sepa- 
rated from  the  acid  solution  of  a  number  of  metals  (copper,  nickel, 
cobalt,  zinc,  etc.)  without  determining  the  other  metals  (excepting 
copper)  at  the  same  time.4 


XIX,  SULPHUR, 

74.   ORES. 

Native  sulphur  (sulphur  earths)  •  iron  pyrites,  FeS27  with  53.33 
S  and  46.47  Fe ;  magnetic  iron  pyrites,  5FeS.Fe2S3,  with  39.5  S ; 
copper  pyrites,  CuFeS2  with  34.89  S. 


1  Classen's  Quan.  Chem.  Anal,  by  Electrolysis. 

2  Ztschft.  f.  Anal.  Chem.  Bd.  19,  p.  17. 

8  Ztschft.  f.  Anal.  Chem.  Bd.  22,  p.  494.  *  Classen. 


ASSAYS  OF  SULPHUR.  277 

75.    ASSAYS    BY    DISTILLATION    FOR    THE    DETERMINATION    OF 
THE   AMOUNT   OF   SULPHUR   WHICH   AN   ORE   MAY   YIELD. 

a.  Sulphur  earths.  —  0.5  to  1  gramme  of  the  ore  is  heated  to  a 
strong  red  heat  in  an  impervious  clay  retort,  on  the  neck  of  which 
is  luted  a  porcelain  tube  (Figs.  45,  46,  p.  62),  when  the  sulphur 
vapors  will  deposit  themselves  in  the  porcelain  tube,  the  end  of 
which  just  dips  in  water.  The  tube  is  then  removed  and  the  sul- 
phur collected,  dried,  and  weighed. 

Gerlach1  conducts  superheated  steam  into  a  glass  retort  con- 
taining the  ore,  from  the  neck  of  which  the  sulphur,  which  passes 
over,  drops  into  a  dish  containing  water. 

6.  Iron  pyrites.  —  2  to  5  grammes,  preferably  mixed  with  the 
same  volume  of  quartz  or  powdered  charcoal  to  prevent  caking, 
are  placed  in  a  glass  tube  30  to  40  centimeters  long  and  13  to  15 
millemeters  wide,  closed  at  one  end.  The  other  end  is  intro- 
duced into  another  glass  tube,  also  closed  at  one  end,  and  the 
substance  is  then  heated  in  a  combustion  furnace  (Fig.  77,  p. 
238),  or  by  another  source  of  heat  (p.  61).  The  end  of  the  tube 
containing  the  sublimed  sulphur  is  cut  off  and  weighed.  The 
sulphur  is  then  volatilized  by  heat,  and  the  tube  again  weighed. 
Pure  iron  pyrites  gives  on  a  large  scale  at  the  utmost  23  per  cent. 
of  sulphur  (7FeS2=6FeS.  FeS2+6S);  copper  pyrites  not  more 
than  9  per  cent.  (Cu2S  +  Fe2S3=Cu2S  +  2F 


76.    ASSAYS   OF  SULPHUR   FOR    THE    DETERMINATION    OF    THE 
QUANTITY  OF   SULPHUR   CONTAINED   IN   A  SUBSTANCE. 

These  assays  may  be  executed  in  order  to  determine  the  yield 
of  an  ore  in  sulphurous  acid,  for  the  manufacture  of  sulphuric 
acid,  or  its  yield  of  sulphur  for  the  formation  of  raw  matt,  for 
controlling  roasting,  etc.  For  this  the  wet  method  is  more  fre- 
quently used  than  the  dry  method. 

A.  Dry  assay  (raw  matt  assay).  —  The  object  of  this  assay  is  to 
determine  the  quantity  of  metallic  sulphides,  especially  iron  sul- 

1  Dingier,  ccxxx.  66. 


278  ASSAYING. 

phide,  contained  in  an  ore,  after  the  oxidized  and  earthy,  etc., 
substances  mixed  with  it  have  been  separated  by  solvent  agents. 

A  mixture  of  5  grammes  of  ore  and  0.5  gramme  of  resin  is  in- 
troduced into  a  crucible  (Fig.  52,  p.  65).  Upon  this  are  placed  10 
to  15  grammes  of  borax,  5  to  10  grammes  of  glass  free  from 
heavy  metals,  a  cover  of  common  salt,  and  a  fragment  of  coal. 
The  charge  is  fused  at  a  bright  red  heat  in  the  muffle  or  wind 
furnace  for  30  to  45  minutes  after  the  "flaming"  has  ceased. 
The  resulting  button  of  iron  sulphide  which  is  brittle,  oxidizes 
and  disintegrates  quickly,  is  carefully  freed  from  the  slag  which 
should  be  well  fused.  It  is  then  weighed  and  broken  up  in  order 
to  recognize  the  presence  of  foreign  metallic  sulphides  by  the  ap- 
pearance of  the  fracture.  When  only  iron  pyrites  are  present, 
this  has  a  fine  grain  'and  speiss  yellow  color ;  with  copper  pyrites, 
brass  yellow ;  with  lead  and  sulphide,  grayish  and  foliated ;  with 
zinc  blende,  radiated  or  foliated,  of  a  sub-metallic  lustre,  and 
blackish-gray ;  with  metallic  antimony  and  arsenic,  a  fine  grain 
and  light  gray. 

Hungary?  If  the  ores  are  easily  fusible,  5  grammes  are 
charged  with  a  flux  composed  of  2  parts  of  calcined  borax  and  1  part 
of  glass  free  from  iron,  by  placing  a  mixture  of  ore  and  11.5 
grammes  of  flux  in  the  bottom  of  the  crucible,  upon  this  23 
grammes  of  flux,  and  on  the  top  8  to  10  grammes  of  common 
salt.  This  is  fused  in  the  muffle  furnace.  When  the  ores  are 
refractory,  1.25  grammes  are  fused  with  the  same  flux,  and  3.2 
grammes  of  a  pure  easily  fusible  concentrated  pyrite  ore,  the  per- 
centage of  matt  contained  in  this  being  afterwards  deducted ;  or, 
with  0.25  to  3.5  grammes  of  copper  as  a  collecting  agent. — Pri- 
bram :  5  grammes  are  mixed  with  f  the  quantity  of  a  flux  con- 
sisting of  10  grammes  of  borax,  2  grammes  of  glass,  and  0.4 
gramme  of  coal  dust.  The  remaining  J  part  of  the  flux  is  strewn 
over  this,  and  on  top  a  cover  of  common  salt  and  fragment  of 
coal.  0.05  gramme  of  copper  may  be  added  to  the  roasted, 
and  as  much  as  0.2  gramme  to  unroasted  ores.  The  crucible 
with  luted  cover  is  gradually  heated  to  a  moderate  red  heat 
in  an  anthracite  furnace  (p.  51),  and  then  fused  for  from  30  to  35 

1  B.  u.  h.  Ztg.  1871,  p.  255. 


SULPHUR — WET   ASSAYS.  279 

minutes  in  a  bright  red  heat. — Slags  with  mechanical  inclosures 
of  matt  are  charged  in  the  following  manner :  30  grammes 
of  slag,  20  grammes  of  borax,  and  50  grammes  of  glass  with  a 
covering  of  common  salt  and  a  fragment  of  coal.  The  charge  is 
fused  for  J  to  £  of  an  hour  at  a  bright  red  heat. 

I>.    Wet  assays.1 

1.  Gravimetric  assays. — 1  gramme  of  ore  is  decomposed  by 
fuming  nitric  acid,  then  nearly  all  the  nitric  acid  removed  by 
boiling.  Hydrochloric  acid  is  now  added  and  heat  is  applied, 
when  the  sulphur  will  be  quickly  dissolved  (the  heating  should 
not  be  continued  too  long,  or  loss  will  ensue  by  the  escape  of  sul- 
phuric acid).  The  solution  is  then  evaporated  to  dryness,  the 
residue  is  heated  with  hydrochloric  acid  in  order  to  expel  the 
nitric  acid  (as  otherwise  the  results  would  be  too  high).  The 
liquid  is  now  diluted  and  filtered,  the  filtrate  precipitated  with 
barium  chloride,  and  the  barium  sulphate  filtered  through  imper- 
vious Swedish  paper,  dried,  ignited,  and  weighed  (BaSO4,  with 
34.356  per  cent.  SO3  and  13.73  per  cent.  S).  The  sulphur  in 
pyrites,  roasted  pyritous  ores,  and  the  same  lixiviated,2  is  deter- 
mined by  heating  0.5  gramme  of  the  substance  in  a  platinum 
crucible,  together  with  10  parts  of  a  mixture  of  2  parts  of  sodium 
carbonate  and  1  part  of  saltpetre.  This  is  lixiviated,  etc.,  and 
finally  precipitated  by  barium  chloride,  etc.,  as  above. — Process 
for  determining  small  quantities  of  sulphur  in  materials  and  pro- 
ducts of  the  iron-works  at  Creuzot.3  The  substance  is  heated  in  a 
porcelain  tube,  and  a  mixture  of  f  of  hydrogen  and  J  carbonic 
acid  is  conducted  over  it.  The  sulphuretted  hydrogen,  which  is 
formed,  is  led  into  an  acid  silver  solution,  and  the  quantity  of 
sulphur  calculated  from  the  weight  of  the  silver  sulphide. 

Gravimetric  determination  of  sulphur  in  pyrites,  according  to 
Lunge.41 — Pour  over  the  finely-powdered  and  sifted  mineral  about 
50  times  its  weight  of  aqua  regia ;  if  reaction  does  not  immediately 
appear,  heat  upon  water  bath  until  a  vigorous  effect  is  produced. 

1  Muspratt's  Chem.  vi.  8. 

2  Fresenius's  Ztschr.  1877,  p.  335.     B.  u.  h.  Ztg.  1877,  p.  241. 

3  Dingier,  ccxxxiii.  (Rollet). 

4  "  Handbuch  d.  Sodaindustrie,"  Braunschweig,  1879,  p.  .92. 


280  ASSAYING. 

Then  at  once  remove  from  water  bath  and  replace  only  when  re- 
action becomes  weaker.  When  the  mineral  is  powdered  sufficiently 
fine  disintegration  is  complete  in  10  or  15  minutes.  If  complete 
disintegration  has  not  been  effected,  add  more  aqua  regia  and  heat. 
Now  add  an  excess  of  HC1  and  evaporate  to  dryness  in  order  to  ex- 
pel all  the  HN03,  as  in  the  presence  of  the  latter  the  results  obtained 
in  precipitating  the  H2S04  with  barium  chloride  are  too  high.  Take 
up  with  water  acidulated  with  HC1,  heat  to  boiling,  and  add  a  hot 
solution  of  barium  chloride,  just  a  little  more  than  sufficient  to  pre- 
cipitate the  H2SOi  present.  The  precipitate  settles  quickly  and  can 
be  filtered  at  once,  wash  with  boiling-  water  acidulated  with  a  few 
drops  of  HC1,  boil  filtrate,  and  after  settling  filter  again.  Repeat 
these  operations  several  times,  but  without  the  addition  of  any  more 
HC1.  Wash  the  precipitate  of  BaSO4  very  thoroughly  and  when 
wash  water  shows  no  further  traces  of  BaCl2  treat  precipitate  and 
filter  in  usual  manner  and  weigh  as  BaS04.  The  latter  should  not 
be  baked  together,  show  an  alkaline  reaction,  or  yield  a  barium  salt 
when  treated  with  hot  dilute  HC1. 

If  the  BaS04  is  colored  yellowish  from  the  presence  of  iron,  it  is 
digested  in  moderately  strong  HC1,  filtered,  washed,  and  again 
ignited.  Or  else  it  can  be  fused  with  soda,  fused  mass  taken  up  with 
water,  filtered,  washed,  and  the  H2S04  again  precipitated  with  BaCl2. 

Fresenius1  observes  that  all  methods,  like  the  above  for  deter- 
mining sulphur  in  pyrites,  have  two  sources  of  error,  mainly  the 
BaS04  contains  ferric  oxide  and  is  sensibly  soluble  in  the  acid  solu- 
tion containing  ferric  chloride.  Hence  by  dissolving  pyrites  in  aqua 
regia  and  precipitating  the  H2S04  with  BaCl2  the  results  are  always 
inaccurate. 

Deutocom?  mixes  1  gramme  of  pyrites  with  8  grammes  of  a  mix- 
ture of  equal  parts  potassium  chlorate,  sodium  carbonate,  and  sodium 
chloride,  and  very  slowly  heats  the  mixture  in  a  large  covered  por- 
celain crucible  until  it  is  thoroughly  dry,  then  fuses  with  a  strong 
heat.  After  cooling  the  mass  is  treated  with  boiling  water  and 
placed  together  with  the  insoluble  residue  into  a  graduated  250  c.c. 
flask.  After  filling  up  and  filtering,  the  H2S04  is  determined  in  50 
c.c.  of  the  filtrate.  The  insoluble  residue  should  retain  no  HaS04. 

Bodewig's  method? — One-half  gramme  of  pyrites  is  treated  in  a 

1  Ztschft.  f.  Anal.  Chem.  Bd.  19,  p.  57. 

2  Ztschft.  f.  Anal.  Chem.  Bd.  19,  p.  313. 

3  Ztschft.  f.  Anal.  Chem.  Bd.  22,  p.  571. 


SULPHUR — WET  ASSAYS.  281 

glass-stoppered  vessel,  of  about  100  c.c.  capacity,  with  30  c.c.  of 
water  and  4  c.c.  of  bromine.  The  stopper  is  quickly  inserted,  and 
the  vessel  shaken  for  five  minutes.  When  oxidation  is  ended,  which 
is  known  by  the  disappearance  of  all  pulverulent  sulphur  adhering 
to  the  sides  of  the  glass,  the  solution  is  emptied  into  a  casserole  and 
most  of  the  bromine  allowed  to  evaporate  in  the  cold.  The  solu- 
tion is  almost  neutralized  with  ammonia,  then  poured  into  an  ex- 
cess of  hot  ammonia  contained  in  a  platinum  dish  and  digested 
from  10  to  15  minutes  at  a  gentle  heat.  The  H^SO^  is  determined 
in  the  filtrate  from  this  in  the  usual  manner.  The  whole  amount  of 
bromine  employed  must  not  be  added  all  at  once,  as  otherwise  there 
may  be  some  loss  of  sulphur  in  the  form  of  H2S.  Some  iron 
volatilizes  as  a  bromide  with  the  excess  of  bromine,  hence  it  cannot 
be  determined  in  the  precipitate  made  by  the  ammonia. 

Determination  of  sulphur  in  pyrites  waste. — According  to  Bock- 
mann,1  in  sulphuric  acid  works  the  pyrites  waste  is  tested  in  regard  to 
its  content  of  sulphur  as  follows  :  Intimately  mix  in  a  platinum  dish  2 
grammes  of  finely  pulverized  waste  writh  25  grammes  of  a  mixture 
of  6  parts  sodium  carbonate  and  1  part  potassium  chlorate.  Fuse 
over  blast  lamp,  take  up  with  water,  and  filter  into  a  tall  beaker 
containing  HC1  in  excess.  After  thoroughly  washing  the  residue 
upon  filter,  the  H2S04  in  the  heated  filtrate  is  precipitated  with  BaCl2. 
The  BaSo4  is  then  treated  and  weighed  in  the  usual  manner. 

Working  test  for  determining  the  residue  of  sulphur  in  the 
roasting  charge? — In  the  upper  Silesian  zinc  works  the  process  of 
roasting  is  controlled  in  the  following  manner  :  The  workman  heats 
a  shovel  in  the  roasting  furnace,  and  when  red  hot  it  is  removed, 
and  about  2  grammes  of  potassium  chlorate  strewed  upon  it.  This 
quickly  melts,  and  upon  the  fused  mass  some  of  the  roasting  charge 
to  be  tested  is  strewn.  If  no  flaming  or  burning  of  separate  grains 
takes  place,  the  blende  is  completely  roasted  ;  if  only  a  grain  here 
and  there  burns,  the  roasting  is  considered  complete  enough,  for  ac- 
cording to  experience  the  roasted  charge  then  contains  only  about 
1  per  cent,  of  sulphur,  which  is  practically  no  detriment  to  the  sub- 
sequent distillation  process.  The  roasted  charge,  however,  should 
not  contain  more  than  1  per  cent,  sulphur. 

1  Ztschft.  f.  Anal.  Chem.  Bd.  21,  p.  90. 

2  Bg.  u.  Httnmsch.  Ztg.  1883,  p.  443. 


282  ASSAYING. 

2.    Volumetric  assays.1 

a.  1  gramme  of  ore  is  intimately  rubbed  together  with  2 
grammes  of  pure  saltpetre,  or  with  3  grammes  of  sodium  carbo- 
nate and  the  same  quantity  of  saltpetre.  The  mixture  is  placed 
in  a  small  dish  of  sheet  iron,  55  millimeters  wide  and  25  milli- 
meters deep,  which  is  placed  in  a  scorifier  (Fig.  47,  p.  64).  It  is 
then  gradually  heated  in  a  red-hot  muffle.  After  fusing  quietly 
from  five  to  eight  minutes,  the  small  dish  is  taken  out  and 
allowed  to  cool  off.  The  mass  contained  in  it  is  then  lixiviated 
with  hot  water,  and  filtered  into  a  small  beaker-glass.  The  resi- 
due is  washed  out  with  as  little  water  as  possible,  and  hydro- 
chloric acid  in  excess  then  gradually  added.  It  is  now  heated  in 
a  sand-bath,  in  order  to  expel  the  nitrous  compounds.  A 
titrated  solution  of  barium  chloride  is  then  added  drop  by 
drop  from  a  burette  to  the  hot  solution  until  no  further  white 
turbidity  is  formed  in  the  supernatant  liquid.  1  cubic  centi- 
meter of  a  normal  solution,  with  0.152  gramme  of  barium  chlo- 
ride, precipitates  0.050  gramme  of  sulphuric  acid,  corresponding 
to  0.020  gramme  of  sulphur ;  or  5  per  cent,  of  sulphuric  acid  and 
2  per  cent,  of  sulphur.  Some  experience  is  required  to  detect 
the  final  reaction.  Indicators  for  this  have  been  proposed,  as, 
for  instance,  potassium  chromate,  by  Wildenstein,  or  filtering  off 
a  few  drops  and  adding  barium  chloride. 

According  to  Wildenstein,  the  solution  containing  sulphuric 
acid  is  diluted  to  a  bulk  of  45  to  55  cubic  centimeters,  to  which 
is  added  a  slight  excess  of  a  titrated  solution  of  barium  chloride. 
It  is  then  boiled  for  a  half  to  one  minute,  a  slight  excess  of 
ammonia  free  from  carbonic  acid  having  first  been  added. 
A  titrated  solution  of  neutral  potassium  chromate  is  now  added  in 
small  quantities,  which  should  not  exceed  J  cubic  centimeter  at  a 
time,  in  order  to  precipitate  the  excess  of  barium  monoxide,  until 
the  liquid,  after  having  been  shaken  and  allowed  to  become  clear, 
shows  a  distinct  yellow  color.  It  is  then  titrated  back  with  a  few 
drops  of  barium  chloride  until  the  fluid  becomes  colorless.  During 
this  operation  the  precipitate'must  be  allowed  to  settle  every  time, 

1  Muspratt's  Chem.  vi.  9.     Fresenius's  Ztschr.  i.  323  (VVildenstein). 


SULPHUR — WET   ASSAYS.  283 

or  a  few  drops  should  be  filtered  off,  and  tested.  Normal  solu- 
tions: 1  cubic  centimeter  of  barium  chloride  =  0.015  gramme  of 
sulphuric  acid,  and  1  cubic  centimeter  of  a  solution  of  potassium 
chromate  =  0.01  gramme  of  sulphuric  acid.  This  assay  gives 
accurate  results  to  within  ^  per  cent,  of  sulphur. 

6.  Metallic  sulphides  decomposable  by  hydrochloric  acid  are 
treated  with  it  in  a  flask  connected  with  a  retort  (Fig.  81,  p. 
271).  The  sulphuretted  hydrogen  developed  is  introduced  into 
a  titrated  solution  of  iodine  in  potassium  iodide  (H2S  +  I2  = 
2HI  +  S),  and  the  unchanged  iodine  titrated  with  sodium  hy- 
posulphite1 (p.  270). 

Volumetric  determination  of  sulphur  in  ores  which  contain 
either  sulphur  alone  or  also  sulphates. — Weil  gives  the  following 
method  :2  Place  1  to  2  grammes  of  the  finely  powdered  ore  in  a 
flask  provided  with  a  cork  through  which  passes  a  bent  tube.  The 
outside  end  of  this  tube  dips  into  an  ammoniacal  solution  of  copper 
of  known  strength.  A  few  small  pieces  of  granulated  zinc  are 
placed  in  the  flask  and  75  c.c.  of  HC1  poured  over  its  contents ; 
quickly  close  the  flask  and  heat.  The  H2S  developed  precipitates 
an  equivalent  portion  of  copper,  and  when  precipitation  ceases,  the 
sulphide  is  allowed  to  settle,  is  filtered  and  washed.  The  object  of 
adding  the  zinc  is  to  dilute  the  H2S  with  hydrogen  and  to  carry  off 
the  last  traces  of  H2S  which  may  remain  in  the  flask  and  glass  tube. 
The  amount  of  filtrate  from  the  precipitated  copper  sulphide  is  care- 
fully measured  and  10  to  20  c.c.  of  it  saturated  with  from  25  to  50 
c.c.  of  HC1.  Heat  to  boiling,  and  when  boiling  titrate  with  a 
standardized  solution  of  stannous  chloride.  The  amount  of  copper 
found  must  of  course  be  calculated  for  the  entire  volume  of  the 
filtrate.  The  amount  of  copper  being  known  from  the  volume  of 
the  copper  solution  used  for  the  precipitation  of  the  H2S,  the 
weight  of  the  precipitated  copper  sulphide  is  found  by  deducting  the 
amount  of  copper  found  remaining  in  the  solution  on  titrating  with 
stannous  chloride.  This  quantity  multiplied  by  0.50393  gives  the 
content  of  sulphur  sought.  The  zinc  added  facilitates  the  action  of 
the  acid  upon  the  ore,  and  if  any  galena  is  present  it  is  also  more 
readily  decomposed,  the  chloride  of  lead  formed  being  reduced  to 
metallic  lead  by  the  zinc. 

1  Dingier,  ccx.  p.  184. 

2  Compt.  Rend.  June  22,  1886.    Genie,  civ.  torn.  ix.  No.  16,  August  14,  1886. 


284  ASSAYING. 

Estimation  of  sulphur  in  metallic  lead.1 — Treat  20  to  30  grammes 
of  very  fine  chips  of  the  lead  with  a  considerable  excess  of  concen- 
trated HC1 ;  sulphur  will  be  set  free  as  H,S.  Pass  this  H2S,  by 
means  of  an  aspirator,  into  bromine  water,  in  which  it  is  decom- 
posed, H2S04  being  formed.  Determine  the  sulphur  in  the  latter 
with  BaCl2,  as  usual.  The  solution  of  the  lead  is  aided  by  gentle 
heat.  A  large  excess  of  HC1  prevents  the  separation  of  lead 
chloride. 


XX,  FUELS, 

77.   FUELS.2 

These  may  be  in  either  of  the  following  forms  :  solid  (raw  or 
natural,  carbonized,  or  artificial,  agglomerated,  or  patent  fuel 
briquetts) ;  or  liquid  (petroleum,  tar-oils) ;  and  gaseous  (natural 
gas,  waste  and  generator  gases,  illuminating  gas). 

The  different  varieties  of  raw  fuel  are,  approximately,  com- 
posed as  follows : — 

c  H  o 

Woody  fibre  (cellulose  =  C6H1005)   .  .  44.44  6.17  49.39 

Peat         .         ...         .         .  .  60.44  5.96  33.60 

Lignite    .        .        .        .    k-    .-       ..  .  66.96  5.27  27.76 

Earthy  brown  coal  .         »         *    '    .  •  74.20  5.89  19.90 

Bituminous  coal,  recent  .    \  .    -   -.  <     .  76.18  5.64  18.07 

"               "     ancient          .       -»  .  90.50  5.05  4.40 

Anthracite  coal,  recent    .         .        '„  .  92.85  3.46  3.19 

"               "    ancient       .    .  -     .  .  94.20  2.50  3.30 

In  order  to  remove  earthy  admixtures  from  fossil  fuel  before 
subjecting  it  to  docimastic  test,  it  is  comminuted  and  stirred  into 
sulphuric  acid  of  1 .4  specific  gravity  (in  soda  manufactories,  in  a 
solution  of  sodium  sulphate).3  The  heavier  earths  will  fall  to  the 
bottom,  while  the  coal  rising  to  the  surface  is  removed  with  a 
spoon,  thoroughly  washed  and  dried. 

1  School  of  Mines,  Quarterly,  vol.  ii.  p  211. 

2  Kerl,  Grtindr.  der  allgemeinen  Huttenkunde,  2  Aufl.  1879,  p.  64.     Muck 
in  B.  u.  h.  Ztg.  1876,  p.  286  (Steinkohlen). 

3  Dingier,  cxc.  76. 


ASSAYS  OF  FUEL.  285 

78.  ASSAYS  OF  FUEL. 

The  examination  extends  to  the  following  points,  on  which  the 
value  of  fuel  chiefly  depends  : — 

1 .  Determination  of  the  amount  of  hydroscopic  water. — 5  grammes 
of  the  powdered  sample  are  placed  in  a  watch-glass  and  heated 
on  a  water-bath  (raw  fuel),  or  (wood-charcoal,  coke)  at  a  high 
temperature  (120°  to  150°  C.,  248°  to  302°  F.)  in  an  air-bath, 
or  on  a  drying  disk  (Fig.  2,  p.  25).     It  is  allowed  to  become  cold 
in  the  desiccator  (Fig.  19,  p.  40),  and  then  weighed:  is  again 
dried  and  weighed  until  two  weighings  agree. 

Air-dried  wood  and  peat  contain  15  to  20  per  cent,  of  water; 
lignite,  10  to  15  per  cent. ;  brown  coal  with  a  conchoidal  fracture, 
10  to  5  per  cent. ;  earthy  coal,  as  much  as  25  per  cent. ;  bitu- 
minous and  anthracite  coal,  fresh  from  the  pit,  1  to  10  per  cent. ; 
wood-charcoal,  10  to  12  per  cent. ;  coke,  5  to  10  per  cent. 

2.  Yield  of  carbon. — 5  to  10  grammes  of  the  material,  either 
in  small  fragments,  or  in  the  form  of  powder,  are  placed  in  a 
covered  crucible  (Fig.  52,  p.  65),  and  gradually  heated  to  a  red 
heat  in  the  muffle  furnace,  until  the  flame  which  shows  itself 
at  the  lid  of  the  crucible  disappears.     The  residue,  upon  cooling, 
is  weighed,  and  (in  tests  of  coal)  the  physical  condition  of  the 
coke  is  observed  at  the  same  time.     This  may  be  more  accurately 
ascertained  by  heating  1  gramme  of  coal  in  a  platinum  crucible 
.40  millimeters  high  with  a  bottom  diameter  of  24  millimeters, 
keeping  the  crucible  at  a  distance  of  3  centimeters  over  the  flame 
of  a  gas-burner.1 

The  yield  of  carbon  will  vary  according  as  the  heat  is  raised 
more  or  less  quickly,  and  with  the  degree  of  temperature,  de- 
creasing as  the  latter  is  more  intense.  Therefore,  if  several 
varieties  of  fuel  are  to  be  compared,  the  carbonization  must  be 
conducted  at  the  same  temperatures.  The  yield  is  generally  less 
than  that  indicated  by  assay  on  the  large  scale.  The  average 
yield  from  wood  charcoal  in  heaps  is  21  to  22  per  cent,  by 
weight ;  from  pine  wood,  55  per  cent.,  and  from  hard  wood,  48 
per  cent,  by  volume ;  and  respectively  25  to  27  and  60  to  65  per 

i  B.  u.  h.  Ztg.  1876,  p.  287. 


286  ,        ASSAYING. 

cent,  in  furnaces ;  from  more  recent  bituminous  coal  as  high  as  60 
per  cent. ;  from  semi-bituminous  coal,  78  to  83  per  cent. ;  from 
anthracite  coal,  84  to  87  per  cent.,  and  from  real  anthracite,  88 
to  93  per  cent,  by  weight. 

Determination  of  the  coking  quality  of  coal  according  to  Richter.1 
1  gramme  of  coal  in  a  finely  powdered  condition  is  mixed  either 
with  0.1,  0.2,  0.3,  etc.,  that  is  to  say,  as  many  times  0.1  gramme  of 
powdered  quartz  as  may  be  necessary  to  just  crush  the  cake  of 
coke  remaining  in  the  covered  porcelain  crucible  after  ignition, 
when  weighed  with  a  0.5  kilogramme  weight  carefully  placed 
upon  it.  If  0.5  gramme  of  powdered  quartz  has  been  used,  the 
coking  quality  of  the  coal  would  be  represented  by  5,  etc. 

3.  Volatile  products    are  determined  from    the  difference   in 
weight  between  the  coke  and  raw  fuel,  after  deducting  the  per- 
centage of  water.     The  amount  of  gas  a  coal  wrill  yield  is  ascer- 
tained by  heating  5  grammes  of  the  sample  in  a  glass  retort  or 
tube.     The  gas  evolved  (after  passing  through  two  wash-bottles 
filled  respectively  with  baryta  wrater  and  lead  acetate  to  absorb 
carbonic  acid  and  sulphuretted  hydrogen)  is  collected  over  mer- 
cury in  a  graduated  cylinder  (Fig.  77,  p.  238). 

4.  Determination  of  the  ash. — The  residue  from  the  assay  for 
carbon  (containing  carbon  and  ash)  is  pulverized  as  fine  as  possible, 
placed  in  a  roasting-dish  (Fig.  8,  p.  32)  and  heated  in  the  muffle, 
which  should  not  be  exposed  to  too  strong  a  draught  of  air,  until 
the  black  particles  have  entirely  disappeared.     The  ash  is  then 
weighed,  and  its  physical  properties  (color,   whether    caked  of 
pulverulent,  etc.)  are  at  the  same  time  examined. 

Gypsum  and  iron  pyrites  undergo  alteration  during  this  opera- 
tion, thus  impairing  the  result  of  the  assay.  This  must  be 
especially  taken  into  consideration  when  a  contract  for  the  pur- 
chase of  coal  is  based  upon  the  minimum  amount  of  ash.2 

In  the  production  of  pig  iron  it  is  important  to  know  the  compo- 
sition of  the  ash  of  the  fuel  used,  as  in  calculating  the  charges  the 
amount  of  silica,  etc.,  in  it  is  an  important  consideration.  A  coal 
containing  pyrites  is  apt  to  contain  small  amounts  of  copper,  which 
exerts  a  very  injurious  effect  upon  the  pig  iron.  A  small  quantity 

1  Dingier,  cxcv.  71.  2  B.  u.  h.  Ztg.  1878,  p.  61  (Muck). 


ASSAYS  OF   FUEL.  287 

of  copper  can  be  readily  detected  in  the  ash  by  moistening  it  with 
HC1  and  heating  it  in  the  non-luminous  part  of  a  gas  flame  or  before 
a  blow-pipe,  whereby  the  flame  will  acquire  an  azure  color.  A 
simpler  method  is  to  throw  a  few  spoonfuls  of  common  salt  on  the 
burning  coals  and  stir.  There  will  immediately  appear  small  azure 
blue  flames  of  burning  carbonic  oxide  containing  cuprous  chloride.1 

Amount  of  ash  in  different  kinds  of  fuel:  Wood,  0.15  to  2  per 
cent.,  an  average  1  per  cent,  (composed  of  about  70  per  cent,  of 
calcium  carbonate  and  20  per  cent,  of  alkaline  carbonates)  ;  wood 
charcoal,  3  to  4  per  cent. ;  peat,  0.5  to  50,  on  an  average  from  6 
to  12  per  cent,  (composed  of,  approximately,  35  per  cent,  of 
argillaceous  sand,  as  much  as  40  per  cent  of  magnesian  gypsum, 
about  30  per  cent,  of  ferric  oxide,  and  3  per  cent,  of  alkalies,  as 
well  as  some  phosphoric  acid  and  chlorine) ;  brown  coal,  as  high 
as  50  per  cent.,  on  an  average  from  5,  to  15  per  cent,  (chiefly 
silicic  acid,  alumina,  ferric  oxide,  lime,  sulphuric  acid,  lesser 
quantities  of  magnesia,  alkalies,  chlorine,  rich  in  sulphur  in  the 
form  of  gypsum  and  iron  pyrites,  poor  in  phosphorus) ;  hard  coal, 
0.5  to  30  per  cent. ;  the  best  coal,  at  an  average  from  4  to  7 ; 
medium  quality  8  to  14 ;  and  poorer  qualities  over  14  per  cent. 
Ash,  mostly  bisilicate  of  alumina  with  lime  (1  to  20  per  cent.), 
ferric  oxide  (1  to  75  per  cent.),  alkalies  (0  to  3  per  cent.),  sulphur 
(0.5  to  2  per  cent.).  Coke,  1  to  30  per  cent,  (good  coke  about  10  per 
cent.),  phosphorus  0.0025  to  0.05  per  cent. — The  amount  ofsidphur* 
contained  in  a  coal  or  its  ash  is  determined  by  fusing  1  gramme 
in  a  platinum  crucible  with  8  grammes  of  saltpetre,  4  grammes 
of  potassium  carbonate,  and  16  grammes  of  common  salt.  The 
fused  mass  is  lixiviated  with  water,  hydrochloric  acid  is  added, 
and  the  mass  then  filtered.  The  filtrate  is  precipitated  with 
barium  chloride,  and  the  resulting  barium  sulphate  containing 
13.8  per  cent,  of  sulphur  is  weighed  (see  also  assays  of  sulphur). 

5.  Determination  of  heating  power. — In  estimating  the  availa- 
bility of  a  fuel  for  a  given  purpose,  it  is  of  the  greatest  importance 

1  Sitzungsterichte  der  konigl.  bohm.  Gesellsch.  d.Wissensch.  p.  9.   Chemi- 
kerzeritung,  1880,  p.  276. 

2  Schwefelbestimmung  in  Steinkohlen,    etc.      Oestr.    Ztschr.  f.  Berg.  u. 
Hiittenwesen,  1874,  p.  11  (Eschka).     Fresenius's  Ztschr.  xii.  32,  178  ;  xiv. 
16  (Sauer).     B.  u.  h.  Ztg.  1875,  p.  228  (Hayes). 


288  ASSAYING. 

to  determine  how  much  heat,  equal  parts  by  weight  (absolute 
heating  effect) ,  or  equal  parts  by  volume  (specific  heating  effect),  of 
different  fuels  will  produce.  The  intensity  of  the  heat  produced 
(pyrometric  heating  effect)  may  also  be  a  point  of  investigation. 

The  latter  may  be  determined  by  calculation  or  by  the  pyro- 
meter/ either  Fischer's2  calorimeter  or  Siemens' 's  electric  pyrometer  ;3 
or  by  means  of  the  fusing  point  of  alloys  by  a  modification  of  Prin- 
sep's  principle.4  The  specific  heating  effect  is  found  by  multiply- 
ing the  absolute  heating  effect  by  the  specific  gravity  of  the  fuel 
in  question.  Berthier's  method  of  determining  the  absolute  heat- 
ing effect  may  be  especially  recommended  for  docimastic  purposes. 

Berthier's  method  of  determining  the  absolute  heating  power  is 
based  upon  Welter's  law,  according  to  which  the  absolute  heating 
power  of  different  combustible  substances  is  proportional  to  the 
amounts  of  oxygen  required  for  their  complete  combustion.  The 
oxygen  is  taken  from  oxides  (lead  oxide),  and  the  quantity  of 
metal  (lead)  set  free  represents  the  quantity  of  liberated  oxygen, 
and  therefore  the  absolute  heating  power. 

Welter's  law  is  based  upon  the  fact  that,  according  to  former 
experiments  by  Rumford,  Despretz,  and  others,  the  absolute  heat- 
ing power  of  carbon  to  hydrogen  is  in  the  proportion  of  1  :  3.03, 
and  the  respective  amounts  of  oxygen  required  for  the  combustion 
of  1  part  of  these  elements  are  in  nearly  the  same  proportion 
(1:3).  But,  according  to  recent  investigations  by  Favre,  Silber- 
mann,  and  others,  the  absolute  heating  powers  of  carbon  and 
hydrogen  are,  respectively,  as  1  : 4.3  ;  and,  therefore,  Welter's 
law  has  become  obsolete,  and  the  results  obtained  by  Berthier's 
method  are  only  approximate.  They  approach  more  closely  to 
the  truth,  the  richer  in  carbon  and  poorer  in  hydrogen  the  fuel 
is,  while  the  results  from  combustible  substances  rich  in  hydrogen 
are  from  ^  to  J  too  low  compared  with  more  accurate  calorime- 
tric  determinations.  His  method  is,  nevertheless,  frequently  used 

1  Kerl,  Grundr.  der  alleg,.  HiUtenkunde,  1879,  p.  85. 

2  Dingier,  ccxxv.  468.     Ber.  d.  deutsch.  chem.  Ges.  1879,  p.  1694. 

3  Dingier,  ccxvii.  291.     B.  u.  h.  Ztg.   1871,  p.  450  ;  1873,  p.  231,  396 ; 
1874,  p.  463  ;  1876,  p.  156  ;  1877,  p.  109. 

4  Freiberger  Jahrb.  1879,  p.  154.      B.  u.  h.  Ztg.  1879,  p.   126  (see  Ap- 
pendix). 


ASSAYS  OF   FUEL.  289 

in  practice,  it  being  very  convenient  and  quickly  executed,  and 
under  the  above-mentioned  conditions  gives  practically  available 
results,  especially  in  the  examination  of  different  varieties  of  the 
same  kind  of  fuel. 

Exactly  1  gramme  of  the  finely  divided  fuel  is  weighed  out 
and  intimately  mixed  with  40  to  50  grammes  of  litharge  finely 
sifted  and  free  from  globules  of  lead,  organic  substances,  and 
minium ;  or,  still  better,  with  70  to  90  grammes  of  white  lead. 
The  mixture  is  covered  with  20  to  25  grammes  of  litharge  (or, 
30  to  40  grammes  of  white  lead),  a  lid  is  placed  upon  the  crucible, 
and  the  charge  gradually  heated  in  the  muffle  furnace  (Fig.  27, 
p.  47)  until  it  is  completely  fused.  The  heat  is  then  increased  for 
a  short  time,  when  the  oxidizable  constituents  of  the  fuel  will  be 
consumed  at  the  expense  of  lead  oxide  and  will  separate  the  more 
lead  the  richer  they  are  in  such  constituents.  After  the  charge 
has  been  fused,  which  requires  from  J  to  £  of  an  hour,  the 
crucible  is  taken  out  and  allowed  to  cool  off.  The  lead  button 
is  then  freed  from  slag,  brushed  off,  and  weighed.  The  resulting 
weight  is  divided  by  the  quantity  of  the  sample  used  in  order  to 
learn  how  much  lead  has  been  reduced  by  it.  The  thermal  value 
of  graphite1  may  also  be  determined  by  this  assay. 

In  the  case  of  combustible  materials  decomposable  at  a  lower 
temperature,  lead  oxychloride,  which  is  more  easily  fusible,  should 
be  used.  It  is  obtained  by  fusing  3  parts  by  weight  of  red 
litharge  together  with  1  part  of  lead  chloride  in  a  Hessian  cruci- 
ble. 1  gramme  of  the  fuel  is  mixed  with  40  grammes  of  the 
oxychloride,  and  the  mixture  covered  with  30  grammes  of  the 
latter. 

One  part  of  pure  carbon  reduces  34  (more  accurately  34.52) 
times  the  quantity  of  lead ;  wood,  12  to  15,  on  an  average  13.95 
parts  (  =  3200  heat  units  =  0.41  per  cent,  carbon) ;  peat  8  to  1 8, 
Irish  varieties  as  much  as  27  parts ;  brown  coal  14  to  26  parts ; 
bituminous  coal  23  to  31  parts,  and  anthracite  26  to  33  parts ;  wood 
charcoal  28  to  33.7  parts  ;  coke  22  to  30  parts  of  lead.  If  the 
fuel  contains  iron  pyrites,  the  quantity  of  lead  reduced  increases 
(1  part  FeS2  reduces  8.72  parts,  and  1  part  FeS,  7.18  parts  of 

i  Kerl,  Thonwaarenindustrie,  1879,  p.  91. 
19 


\ 

290  ASSAYING. 

lead  from  litharge).     Suppose  p  to  be  the  weight  of  the  lead 
button,  the  heating  power  in  calories  or  heat  units  is  expressed 

orvorv 

by  x  =  ^>TT  P  =  234  p.     In  case  the  fuel  contains  a  large  amount 

of  hydrogen,  this  value  must  be  multiplied  with  a  co-efficient 
lying  between  1  and  -f . 

Suppose  100  kilogrammes  of  coal  must  be  replaced  by  wood, 
in  a  reverberatory  furnace,  in  some  smelting  process.  How  much 
of  the  latter  must  be  taken?  The  absolute  heating  power  of 
both  must  be  determined  according  to  Berihier's  method,  by 
which  they  are  capable  of  reducing,  respectively,  24  and  14 
parts  of  lead.  Then  14  :  24  =  100  :  x  and  x  =  170  kilogrammes 
(374  pounds)  of  wood  supply  the  place  of  100  kilogrammes  (220 
pounds)  of  coal.  If  the  quantities  of  fuel  are  to  be  determined 
by  the  volume,  it  is  only  necessary  to  multiply  the  above  numbers, 
24  and  14,  by  the  specific  gravity  of  the  fuel  in  question,  and  to 
formulate  the  resulting  products  into  a  similar  proportion.  • 

6.  Determination  of  the  sulphur. — According  to  Drown, *a  solution 
of  sodium  hydrate,  of  1.25  sp.  gr.,  is  saturated  with  bromine.  If 
an  excess  of  bromine  is  used,  it  must  be  neutralized  by  the  addition 
of  a  little  more  sodium  hydrate.  The  finely  powdered  coal  is 
moistened  with  25  c.c.  of  this  solution  and  heated,  then  HC1  is 
added  cautiously  to  just  acid  reaction.  This  operation  is  repeated 
with  another  25  c.c.  of  the  alkaline  solution  and  again  made  acid. 
The  mixture  should  be  kept  hot.  The  contents  of  the  beaker  or 
dish  are  then  evaporated  to  dryness  to  separate  silica  and  taken  up 
with  dilute  HC1.  The  H2S04  is  precipitated  with  the  usual  precau- 
tions by  barium  chloride.  Instead  of  using  pure  bromine  a  saturated 
solution  of  bromine  in  potassium  bromide  may  be  used  with  equally 
good  effect.  According  to  Atkinson,2  the  content  of  sulphur  is  de- 
termined as  follows :  Dry  the  finely  powdered  fuel  at  100°  C.,  mix 
one  gramme  of  it  with  5  grammes  of  anhydrous  sodium  carbonate, 
introduced  into  a  flat  platinum  dish  and  spread  uniformly  over 
bottom.  Heat  very  slowly  in  muffle,  for  not  over  a  half  hour,  to 
clear  cherry-redness.  Allow  the  air  to  enter  muffle  freely,  the  heat 
must  not  be  sufficient  to  sinter  or  fuse  the  sodium  carbonate.  At 

1  Trans.  Am.  Inst.  M.  E.,  vol.  viii.  p.  569,  and  vol.  ix.  p.  656. 

2  Journ.  Soc.  Chein.  Ind.  1886,  p.  154. 


EXAMINATION   OF  FURNACE  GASES.  291 

the  end  of  the  half  hour  the  sulphur  will  be  oxidized  and  absorbed 
by  the  sodium  carbonate,  the  carbon  will  also  be  all  burnt  off.  Lix- 
iviate with  150  c.c.  of  hot  water.  When  the  insoluble  portion  has 
settled,  filter,  wash  with  hot  water  containing  some  pure  sodium  chlo- 
ride, rinse  precipitate  with  the  same  solution  acidulated  with  10  c.c. 
of  pure  HC1,  boil,  and  precipitate  in  usual  manner  with  barium 
chloride.  It  is  claimed  that  the  addition  of  the  sodium  chloride 
solution  prevents  the  passage  of  the  finely  divided  ash  through  the 
filter. 

7.  Physical  and  chemical  behavior. — The  following  points  must 
be  considered  as  exerting  an  influence  upon  the  action  of  com- 
bustible substances  in  the  fire,  during  transportation,  etc. :  Struc- 
ture, density  (compactness),  form  and  size  of  the  lumps,  specific 
gravity,  behavior  when  thrown  into  the  glowing  muffle,  or  in 
the  furnace  (whether  they  kindle  easily  or  with  difficulty,  burn 
quietly  or  fly  into  pieces,  whether  the  flame  is  short  or  long,  or 
more  or  less  smoking,  the  liberation  of  odors,  brittleness,  etc.), 
chemical  composition  of  the  fuel,  and  of  the  pulverulent,  sintered, 
or  clinkered  ash,  etc. 

79.   EXAMINATION  OF   FURNACE  GASES. 

To  be  able  to  judge  the  processes  taking  place  during  combus- 
tion,1 the  velocity  of  the  flue  gases,  and  the  amount  of  air  passing 
through  the  furnace  are  determined  by  an  anemometer?  the 
strength  of  the  draught  by  a  draught  meter*  the  intensity  of  the 
heat  by  a  pyrometer*  and  the  amount  of  carbonic  acid,  carbonic 
oxide,  and  free  oxygen  in  the  furnace  gases  are  ascertained — 

1.  By  means  of  Or  sat7  s  apparatus.5 — With   some  experience 

1  Kerl,  Thonwaarenindustrie,  1879,  p.  301. 

2  Topfur-u.  Ziegler-Ztg.  1878,  No.  1. 

3  Dingier,  clxxi.  43  (List).  Notizbl.  der  deutsch.  Ver.  f.  Fabrikation  von 
Ziegeln  u.  s.  w.  ix.  96;  xi.  191  ;  xiii.  40,  42.     Topfer-u.  Ziegler-Ztg.  1877, 
No.  46. 

4  Kerl,  Grundr.  d.  allg.  Huttenkunde,  1879,   p.  85.     Mitchell,    Practical 
Assaying,  1888,  p.  167. 

5  Fichet-Ramdohr,  Gasfeuerung,  Halle,  1875.     Ann.  des  mines,  vol.  viii. 
livr.  6  de  1875.     B.  u.  h.  Ztg.  1874,  p.  232 ;  1875,  p.  143  ;  1876,  p.  72  ;  1877, 
p.  147.     Dingier,  ccxix.  420  (Weinhold).     Fresenius's  Ztschr.  1877,  p.  343 


292 


ASSAYING. 


and  intelligence  this  apparatus  gives  results  available  for  practi- 
cal purposes,  even  in  unscientific  hands.  It  is  based  upon  the 
principle,  that  a  measured  volume  of  gas  is  conducted  through 
agents  for  the  absorption  of  its  principal  constituents  (caustic 
potassa  for  carbonic  acid,  potassium  pyrogallate  for  oxygen,  and 
solution  of  cuprous  chloride  for  carbonic  oxide),  the  volume  of 
gas  remaining  after  each  absorption  being  measured,  when  the 
amount  of  each  will  be  ascertained  from  the  diiference.  The  ap- 

Figs.  83  and  84. 


paratus  is  placed  in  a  portable  wooden  case,  and,  according  to 
Fischer's  latest  construction,  is  arranged  as  follows,  (Fig.  83) : — 
A  is  a  burette  inclosed  in  a  glass  cylinder.     Its  lower  end  is 

(Seyberth).  Oest.  Ztschr.  1877,  No.  11,  13,  16.  Ztschr.  de  Ver.  deutsch. 
Ing.  xx.  318.  Dingier,  ccxxvii.  258  ;  ccxxix.  262  (Fischer.)  Winkler,  Anlei- 
tung  z.  Chem.  Untersuchuug  der  Industriegase,  2  Abth.,  1877,  p.  1859. 


EXAMINATION  OF   FURNACE   GASES.  293 

connected  with  the  water  flask  E  by  means  of  a  rubber  tube. 
The  burette  is  capable  of  holding  100  cubic  centimeters.  Its 
lower  part  holding  40  cubic  centimeters  is  graduated  to  one-fifth 
cubic  centimeter,  and  the  upper  part  in  whole  cubic  centimeters. 
B  CD  are  the  absorption  vessels  (B  for  caustic  potassa,  C for 
potassium  pyrogallate,  and  D  for  solution  of  cuprous  chloride,  or 
fluid  obtained  by  shaking  copper  hammer  scale  with  a  mixture  of 
equal  volumes  of  ammonia  and  cold  saturated  solution  of  sal  am- 
moniac). The  vessels  are  filled  with  fine  glass  tubes  and  con- 
nected with  the  burette  by  means  of  a  system  of  thick-walled 
capillary  tubes,  a  b  c  are  plain  cocks ;  d  is  a  Winkler  cock  (Fig. 
84,  B),  which  besides  having  a  simple  perforation  is  also  cut 
lengthwise.  The  outer  end,  a,  is  connected  with  an  aspirator  by 
means  of  a  rubber  tube.  When  the  cock  is  properly  set,  the  tube 
e  (which  is  provided  with  a  little  water,  and  loosely  filled  with 
cotton,  in  order  to  saturate  the  gas  with  water  vapor  and  to  re- 
tain dust),  and  the  gas-conducting  tube  connected  with  it,  can 
then  be  filled  with  the  gas  to  be  examined.  * 

The  operation  is  conducted  as  follows :  The  cock  d  is  set  so 
that  it  communicates  with  the  outer  air.  The  flask  E,  filled  with 
water,  is  raised  so  that  A  will  become  completely  filled  with 
water,  the  air  escaping  from  d.  d  is  then  closed  towards  A.  The 
cock  a  is  now  opened  and  the  flask  E  lowered,  whereby  the  ab- 
sorption vessel  B  is  filled  with  the  absorbing  liquid  (potassium 
hydrate)  to  the  mark  immediately  below  the  cock  a,  whereupon 
this  is  closed.  C  is  filled  in  a  similar  manner  with  potassium 
pyrogallate,  and  D  with  a  solution  of  cuprous  chloride  from 
vessels  of  equal  size  communicating  with  and  placed  behind 
them.  The  furnace  gas  to  be  examined  is  aspirated  through  the 
aspirator,  and  the  connection  between  e  and  A  is  established  by 
the  cock  d,  after  the  burette  A  has  been  completely  filled  by 
raising  the  flask  E.  The  latter  is  then  lowered  when  A  will 
be  become  filled  with  the  gas.  d  being  properly  set,  the  gas  is 
allowed  to  escape  by  again  raising  E,  in  order  to  expel  any  small 
quantities  of  air  which  may  still  be  contained  in  the  capillary 
tubes.  After  A  has  in  this  manner  been  filled  with  gas,  this  is 
successively  forced  by  the  same  manipulation  through  J5,  CJ  and 


294 


ASSAYING. 


T 
$=3 


D,  and  each  time  returned  to  A  in  order  to  measure  the  volume 
of  gas  which  has  been  absorbed  respectively  in  B,  C,  and  D. 

Orsat  has  further  enlarged  his  apparatus  so  that  hydrogen  and 
carburetted  hydrogen  can  be  also  determined.1  An  apparatus 
for  examining,  by  SchwaeJchofer,2  has  recently  been  recommended, 
it  being  claimed  that  it  is  less  easily  broken  and  safer  to  handle 
than  Orsat's. 

2.  By  means  of  Bunte's  burette3  (Fig.  85). — An  unlimited 
number  of  absorbing  agents  can  be  used  in  this  apparatus,  as  it 
allows  of  the  removal  of  the  absorbing  liquids  from  the  burette 

without  a  loss  of  gas  every 
time  after  they  have  been 

Vused,  and  further  permits  the 
\m  gas  inclosed  in  the  burette  to 

be  brought,  after  each  absorp- 
tion, to  the  same  pressure. 
A  is  a  burette  divided  from 
the  Winlder  cock  a  to  the 
common  cock  b  into  some- 
what more  than  110  cubic 
centimeters  and  fractions,  t 
is  a  funnel  forming  the  upper 
part  of  the  burette,  having  a 
capacity  of  25  cubic  centi- 
meters to  the  mark  m.  The 
burette  A  is  filled  with  gas 
by  connecting  a  with  the  gas- 
conductor  by  means  of  a  rub- 
ber tube,  and  aspirating  the 
gas  through  b  until  all  the  air 
has  been  expelled  from  A.  a 
and  b  are  then  closed,  and  a  rub- 

1  Ann.  d.  min.  1875,  t.  viii.  p.  501.     Oest.  Ztschr.  1877,  No.  13.     B.  u.  h. 
Ztg.  1878,  123.    Dingier,  ccxxi.  284  ;  ccxxvii.  171  (Fischer).     Winkler,  Anl. 
d.  chem,  Untersuchung  der  Industriegase,  2  Thl.  p.  198. 

2  Ztschr.  der  berg.  u.  huttenm  Ver.   fur.  Steyermark  u.  Karnthen,  1878, 
Nos.  3-6,  p.  78. 

3  Dingier,  ccxxvii.  167  ;  ccxxviii.  46. 


EXAMINATION   OF   FURNACE   GASES.  295 

ber  tube,  plugged  at  one  end  with  a  small  glass  rod,  is  pushed  over 
the  point  of  a.  In  order  to  bring  the  volume  of  gas  in  the  burette  to 
100  cubic  centimeters  under  a  known  pressure,  water  is  forced  into 
the  burette  up  to  the  0  point  by  means  of  a  rubber  hose  filled  com- 
pletely with  water,  and  connected  with  the  funnel  T  and  the 
point  of  the  burette,  b  is  then  closed  and  a  opened  towards  m, 
whereby  a  part  of  the  gas  escapes,  and  the  inclosed  remaining 
part  stands  under  the  pressure  of  the  atmosphere  and  a  column  of 
water  a  few  cubic  centimeters  high.  The  gas  can  in  a  similar 
manner  be  brought  under  equal  conditions  of  pressure  at  any 
desired  position  of  the  liquid  in  the  burette,  and  a  correction  for 
the  pressure,  which  is  made  the  same  at  every  reading,  is  not  re- 
quired in  the  customary  statement  of  the  results  of  the  experi- 
ments in  per  cents,  of  the  total  volume. 

The  following  is  the  process  of  manipulating  when  furnace 
gases  in  the  burette  contain  carbonic  acid,  carbonic  oxide,  and 
oxygen.  The  minutely  perforated  point  b  of  the  burette  is 
connected  with  the  flask  F  by  the  rubber  tube  r.  The  cock  b  is 
then  opened  and  air  drawn  out  through  the  tube  s  by  suction, 
whereby  water  is  drawn  from  the  burette  A  to  F,  and  then  b  is 
immediately  closed.  The  flask  F  is  removed  from  the  burette, 
and  the  point  of  this  is  dipped  into  a  dish  containing  solution  of 
potassium  hydrate.  When  the  cock  b  is  opened  this  enters  A  and 
replaces  the  water  drawn  out.  The  burette  is  held  by  its  ex- 
tremities and  gently  shaken  for  the  absorption  of  the  carbonic 
acid.  As  soon  as  this  has  been  accomplished  t  is  connected  with 
A  by  the  cock  a,  whereby  water  enters  into  A  until  the  pressure 
is  completely  equalized.  The  volume  of  carbonic  acid,  which 
has  disappeared,  is  read  off  on  the  burette.  The  oxygen  is  de- 
termined in  a  similar  manner  by  withdrawing  a  part  of  the 
potassium  hydrate  by  suction,  and  allowing  potassium  pyrogallate 
to  enter ;  while  for  the  determination  of  the  carbonic  oxide  the 
potassium  pyrogallate  must  be  entirely  removed  from  the  burette 
by  repeatedly  aspirating  the  liquid  from  A  through  6,  and  al- 
lowing water  to  flow  in  through  a  from  t  until  the  absorbing 
agent  has  been  entirely  removed,  when  solution  of  cuprous  chlo- 
ride is  introduced  in  the  manner  indicated. 


APPENDIX. 


A.   TABULAR  SYNOPSES. 
1.  Atomic  Weights. 


Old 
equivalent 
weights. 

New 

atomic 
weights. 

Old 
equivalent 
weights. 

New 
atomic 
weights. 

Aluminium       .     . 

13.7 

27.4 

Mercury       .     .     . 

100 

200 

Antimony    .     .     . 

122 

122 

Molybdenum    .     . 

46 

.  96 

Arsenic  .... 

75 

75 

Nickel     .... 

29.3 

58.6 

Barium  .... 

68.5 

137 

Niobium      .     .     . 

47 

94 

Beryllium    .     .     . 

4.7 

9.3 

Nitrogen      .     .     . 

14 

14 

Bismuth       .     .     . 

210 

210 

Osmium       .     .     . 

99.2 

199.4 

Boron      .... 

11 

11 

Oxygen  .... 

8 

16 

Bromine       .     .     . 

80 

80 

Palladium   .     .     . 

53.3 

106.6 

Cadmium     .     .     . 

56 

112 

Phosphorus      .     . 

31 

31 

Caesium        .     .     . 

133 

133 

Platinum     .     .     . 

99 

198 

Calcium       .     .     . 

20 

40 

Potassium    .     .     . 

39 

39.1 

Carbon    .... 

6 

12 

Rhodium      .     .     . 

52.2 

104.4 

Cerium    .... 



91.2 

Rubidium    .     .     . 

85.5 

85.5 

Chlorine       .     .     . 

35.5 

35.5 

Ruthenium       .     . 

52.2 

104.4 

Chromium   .     .     . 

26.1 

52.2 

Selenium     .     .     . 

39.7 

79.4 

Cobalt     .... 

29.5 

59 

Silicium       .     .     . 

14 

28 

Copper    .... 
Didymium  .     .     . 

31.7 

48 

63.4 
95 

Silver      .... 
Sodium   .... 

108 
23 

108 
23 

Erbium  .... 

56.3 

112.6 

Strontium    .     .     . 

43.8 

87.6 

Fluorine       .     .     . 

19 

19 

Sulphur       .     .     . 

16 

32 

Gallium       .     .     . 

__ 

68.8 

.  Tautalium   .     .     . 

91 

182 

Gold  

197 

197 

Tellurium    .     .     . 

64 

128 

Hydrogen     .     .     . 

1 

1 

Thallium     .     .     . 

204 

204 

Indium   .     .     *  „  . 

56.7 

113.4 

Thorium      .     .     . 

— 

232.4 

Iodine     .... 

127 

127 

Tin     

59 

118 

Iridiurn        .     .     . 

99 

198 

Titanium     .     .     . 

25 

50 

Iron    ..... 

28 

56 

Uranium      .     .     . 

60 

120 

Lauthanium     .  -, 

46 

93 

Vanadium  .     .     . 

51.3 

Lead        .     .     .     . 

103.5 

207 

Wolfram      .     .     . 

92 

184 

Lithium       .     .     . 

7 

7 

Yttrium       .     .     . 

30.85 

61.7 

^I  3i  &  n  6  s  i  urn 

12 

24 

32.6 

65.2 

Manganese        .     • 

27.5 

55 

Zirconium    .     .     . 

44.8 

89.6 

298 


APPENDIX. 


2.   Fusing  Points  of  Metals  and  Furnace  Products,1  Glowing 
Temperatures. 


> 

Fusing 

point 
(Celsius.) 

Fusing 
point 
(Fahr.). 

Glowing 
emperature 
(Celsius). 

Glowing 
temperature 

(Fahr.). 

Tin       .         .                  .    *    .         . 

228° 

442.4° 

264 

507.2 

Thallium     .         .         . 

290 

554 

Cadmium  (455°  C.,  851°  F.)  (boil- 

ing point  891°  C.,  1635.8°  F.) 

320 

608 

Lead    ... 

335 

635 

Zinc  (boiling  point   according  to 

Becquerell  891°  C.,  1635.8°  F., 

according  to  Deville  1040°  C., 

1904°  F.)           .... 

412 

773.6 

Antimony     .         .  '.'     .         . 

432 

809.6 

Incipient  redness 





525° 

977° 

Dark  redness 





700 

1292 

Aluminium           .... 

700 

1292 

Incipient  cherry-redness 





800 

1472 

Strong  cherry  -redness  . 





900 

1652 

Bronze          ..... 

900 

1652 

Litharge       ..... 

954 

1749.2 

Complete  cherry-redness 





1000 

1832 

Silver  (according    to   Becquerell 

916°  C.,  1680.8°  F.) 

1000 

1832 

Copper  matt         .... 

1002 

1835.6 

1015 

1859 

Lead  matt    ..... 

1027 

1880.6 

Black  copper        .... 

1027 

1880.6 

Raw  matt     ..... 

1047 

1916.6 

Lead  speiss           .... 

1062 

1943.6 

Copper          ..... 

1090 

1994 

Gold   (according   to    Becquerell 

1037°  C.,  1898.6°  F.) 

1200 

2192 

Bright  redness       .         .     ^    . 





1200 

2192 

White  heat  .... 





1300 

2372 

Lead  and  lead  matt  slag 

1315-1330 

2399-2426 

Raw  slag      ....         . 

1330-1360 

2426-2480 

Black  copper  slag 

1345 

2453 

Blast-furnace  slag 

1390-1430 

2534-2606 

Cobalt  (1400°  C.,  2552°  F.). 

Strong  white  heat        •  .  -    . 

__ 



1400 

2552 

Dazzling  white  heat      .    '     * 





1500-1600 

2732-2912 

Cast-iron   (according   to  Becque- 

rell 1050°  to  1200°  C.,  1922°  to 

2192°  F.)           .         .         .         . 

1500-1700 

2732-3092 

White  crystalline  pig-iron  accord- 

ing to  v.  Tunner 

1600 

2912 

Gray  charcoal  pig-iron  according 

to  v.  Tunner    .... 

1700 

3092 

1  The  older  fusing  points  are  mostly  according  to  Plattner  ;  those  inclosed  in 
brackets  are  newer,  according  to  Becquerell. 


TABULAR   SYNOPSES. 


299 


Fusing 
point 
(Celsius.) 

Fusing 
point 
(Fahr.). 

Glowing 
temperature 
(Celsius.) 

Glowing 
temperature 
(Fahr.). 

Palladium  (according  to  Becque- 

rell  1360°  to  1380°  C.,  2480°  to 

2516°  F.)           .... 

1600° 

2912° 

Nickel  (1600°  C.,  2912°  F.) 

Wolfram  (1700°  C.,  3092°  F.)      . 

Manganese    (according    to    John 

1500°  C.,  2732°  F.,  according  to 

Becquerell  1600°  C.,  2912°  F.) 

Uranium    and    molybdenum 

(1600°  C.,  2912°  F.) 

Chromium  (1700°  C.,  3092°  F.)   . 

Steel    (according    to    Becquerell 

1300°  to  1400°  C.,  according  to 

v.  Tunner  1850°  C.,  3362°  F.) 

1700-1900 

3092-3452 

Malleable  iron  (according  to  Bec- 

querell 1600°  C.,  2912°  F.)       . 

1900-2100 

3452-3812 

Platinum  (according    to   Debray 

2000°  C.,  3632°  F.,   according 

to  Becquerell  1460°  to  1480°  C., 

2660°  to  2696°  F.)     . 

2534 

4593.2 

Iridium  (2400°  C.,  4352°  F.) 

Plattner's  method  is  based  upon  Prinsep's  principle  (deter- 
mination of  temperatures  by  the  fusing  points  of  alloys),  but  his 
deductions  are  untenable,  although  probably  approximate  for  the 
average  of  commencing  fusion  of  substances.  The  determination 
of  the  fusing  point  of  the  old  furnace  products  of  the  Freiberg 
smelting  works  is  also  of  but  little  importance  at  the  present  time, 
as  these  products  have  lately  been  materially  changed  by  new 
processes. 

Erhard  and  Schertel  have  recently  made  experiments  with  the 
aid  of  their  improved  pyrometer  to  determine  the  fusing  points 
of  metals,  alloys,  furnace  products,  silicates,  minerals,  and  rocks. 
As  these  may  be  considered  at  the  present  as  the  most  reliable, 
we  give  them  in  the  following  table  : — 


300 


APPENDIX. 


3.  Fusing  Points  of  Metals,  Alloys,  Furnace  Products,  Rocks,  and 
Silicates,  according  to  ErJiard  and  Schertel.1 

a.  Metals  and  Alloys. 


Degrees  Celsius. 

Degrees  Fahrenheit. 

./ 

954 

1749.2 

80  A 

g     20  A 

u   .    .   V 

975 

1787 

60 

40 

.    . 

995 

1823 

40 

60 

"...    ! 

1020 

1868 

20 

80 

... 

1045. 

1913 

£ 

1075 

1967 

95  A 

u      5  P 

. 

1100 

2012 

90 

10 

... 

1130 

2066 

85 

15 

... 

1160 

2120 

80 

20 

... 

1190 

2174 

75 

25 

... 

1220 

2228 

70 

30 

. 

1255 

2291 

65 

35 

, 

1285 

2345 

60 

40 

. 

1320 

2408 

55 

45 

'          .         •         • 

1350 

2462 

50 

50 

... 

1385 

2525 

45 

55 

... 

1420 

2588 

40 

60 

... 

1460 

2660 

35 

65 

•         •         • 

1495 

2723 

30 

70 

1535 

2795 

25 

75 

. 

1570 

2858 

20 

80 

. 

1610 

2930 

15 

85 

: 

•  1650 

3002 

10 

90 

... 

1690 

3074 

5 

95 

•     .     • 

1730 

3146 

I 

't 

. 

1775 

3227 

i  Freiberger  Jahrb.  1879,  p.  154.     B.  u.  h.  Ztg.  1879,  p. 


126. 


HARZ  WORKING  ASSAYS. 


301 


b.  Furnace  Products  and  Gangues. 


Corresponding 
alloy. 

Temperature 
degrees 
Celsius. 

Temperature 
degrees 
Fahrenheit. 

Slag  from  working  the  ores   in   the 
Muldner  smelting  works  (porous) 
The  same  rich  in  zinc  (porous)     .     . 
The  same  two  slags  entirely  fused 
Concentration  slag  of  copper  matt 
Melaphyre  from  Mulatto       .     .     .     . 
Pitchstoue  from  Arran     

J70AU 

90  Au 

80  " 

j  94  " 

60   " 
50   " 

49    " 

59    " 

75   " 

67   " 
68   " 

77   " 

30  Ag 

10  Pt 

20  Ag 

6Pt 

40   " 
50   " 

51    " 

41    " 

25    " 

33   " 

32  " 

23   « 

1030 

1130 
1045 

1106 

1300 
1400 

1392 
formation 
temp. 

1326 
1220 

1273 
1267 

1208 

1886 

2066 
1913 

2022.8 

2372 
2552 

2537.6 

2418.8 
2228 

2323.4 
2312.6 

2206.4 

Temperature  in  the  porcelain  kiln     . 
Blast-furnace   slag  (50Si02,  17A1203, 
3FeO,  SOCaO)      ....... 

Fusing  point  77Au  23Pt  =  1208°  C. 
(2206.4°  F.). 
Freiberg    raw   slag   (48Si02,    9A1203, 
37FeO,  4.5CaO,  1.5MgO)  .... 
Freiberg  lead  slag  (36.5Si02,  40.5FeO, 
8.5A1203,  4CaO,  3MgO,  7.5  BaO)     . 
Fusing  point  85Au  15Pt  =  1160°  C. 
(2120°  F.). 
Freiberg  black  copper  slag  (32.7Si02, 
60  3FeO   7A1203)      

Fusing  point  83Au  17Pt  =  1172°  C. 
(2141.6°  F.). 
Raw  slag  from  3.45  dry  ore  and  5.25 
lead  slag    

2.4  raw  matt,  fusing  point  83Au 
17Pt  =  1172°  C.  (2141.6°  F.). 
Lead    slag   from   2.34    roasted    lead 
ore,   1.80  roasted  raw  matt,  5.00 
lead  slag,  0.30  powdered  coke   .     . 

B.  LOWER  HARZ  WORKING  ASSAYS. 

According  to  Brauning,1  the  following  methods  are  used  in  the 
Oker  assay  laboratory  for  assaying  the  Rammdsberg  ores  and  the 
furnace  products  obtained  from  them,  after  25,000  to  75,000 
kilogrammes  have  been  broken  into  pieces  the  size  of  a  fist.  A 
few  grammes  of  samples  are  taken  by  crossing  ;  these  are  commi- 
nuted in  a  stamping-mill,  powdered  fine  in  a  mortar,  and  sifted. 

a.  Lead  (p.  88). — 3.75  to  7.5  grammes  of  the  ore  are  decom- 
posed with  aqua  regia  and  evaporated  with  addition  of  sulphuric 
acid.  The  mass  is  then  digested  with  diluted  sulphuric  acid,  and 


1  Zeitschr.  f.  Berg-,  Hiitten-,  u.  Salinenwesen  im  Preuss.  Staate,  Bd.  25. 


302  APPENDIX. 

filtered.  The  filtrate  is  placed  on  the  roasting-dish  and  dried 
under  the  muffle.  The  mass  is  then  mixed  with  three  times  the 
quantity  of  black  flux  (1  part  of  saltpetre  and  2  parts  of  argol), 
and  placed  in  a  crucible  (Fig.  49,  p.  64).  0.75  to  1.13  grammes 
of  iron  wire  and  a  thin  covering  of  common  salt  are  added,  and 
the  charge  is  fused  under  the  muffle  for  from  fifteen  to  twenty 
minutes. 

b.  Copper. — The  filtrate  from  the  test  with  sulphuric  acid  (a) 
is  diluted  to  the  bulk  of  1  liter.  250  cubic  centimeters  of  this 
are  taken  and  treated  with  10  to  15  cubic  centimeters  of  nitric 
acid  of  1.2  specific  gravity.  The  solution  is  then  precipitated  by 
sulphuretted  hydrogen,  and  the  precipitate,  in  case  its  color  indi- 
cates the  presence  of  considerable  quantities  of  antimony  and 
arsenic,  is  treated  with  sodium  sulphide.  The  residue  of  copper 
sulphide  is  dissolved  in  20  to  30  cubic  centimeters  of  moderately 
diluted  nitric  acid.  This  is  diluted  with  water,  filtered,  and  the 
copper  precipitated  by  electrolysis  (p.  110). — Swedish  assay  for 
the  determination  of  copper  in  intermediate  products.  The  object 
is  attained  more  quickly  by  this  method,  but  it  is  done  at  the 
expense  of  accuracy.  3.75  grammes  of  the  assay  sample  are 
decomposed  with  aqua  regia,  and  evaporated  to  dryness  with 
sulphuric  acid.  The  dry  mass  is  then  taken  up  with  some  diluted 
sulphuric  acid,  filtered,  and  the  copper  precipitated  with  zinc. 
The  precipitated  copper  is  then  ignited  under  the  muffle. — Heine's 
eolorimetric  assay  (p.  125)  for  products  poor  in  copper  (slags,  lix- 
iviation  residues).  3.75  grammes  of  the  substance  are  decom- 
posed by  means  of  aqua  regia.  The  solution  is  supersaturated 
with  ammonia  and  filtered.  It  is  then  diluted  to  a  known  volume 
and  compared  with  standard  solutions. 

G.  Iron. — The  filtrate  from  the  precipitation  with  sulphuretted 
hydrogen  (6)  is  oxidized  with  nitric  acid.  It  is  then  evaporated 
to  a  small  volume,  and  precipitated  with  ammonia.  The  pre- 
cipitate is  dissolved  in  hydrochloric  acid,  reduced  with  stannous 
chloride,  and  the  excess  of  stannous  chloride  is  titrated  back  with 
solution  of  iodine  (Kerfs  Eisenprobirkunst,  1875,  p.  16). 

d.  Zinc  (p.  218). — The  filtrate  from  the  iron  precipitate  is 
slightly  acidulated  with  hydrochloric  acid,  and  then  tested  for 
zinc  with  potassium  ferrocyanide  by  the  volumetric  method. 


SCHAFFNER'S  ASSAY  OF  ZINC.  303 

e.  Silver. — 3.75  grammes  of  ore,  etc.,  are  placed  in  a  scorifier 
with  a  mixture  of  37.5  grammes  of  granulated  lead  and  0.55  to 
0.75  grammes  of  borax,  and  with  a  cover  of  0.37  gramme  of 
borax,  and  the  charge  fused.  The  lead  buttons  are  cupelled  in 
cupels  made  of  3  parts  of  wood-ash  and  1  part  bone-meal.  The 
buttons  of  silver  are  weighed. — Black  copper  and  crude  copper 
are  fused  with  twenty  times  the  quantity  of  granulated  lead. 
The  assay  of  fine  silver  is  executed  according  to  Valhard's 
method,  it  being  simpler  and  more  expeditious  than  that  of  Gay- 
Lussae,  and  equals  the  last-named  in  accuracy. 

/.  Gold. — The  buttons  obtained  from  fusing  with  lead  (see  e) 
are  dissolved  in  nitric  acid  (free  from  chlorine)  of  1.2  specific 
gravity.  The  solution  is  carefully  heated  to  the  boiling  point, 
and,  when  the  action  of  the  acid  can  no  longer  be  perceived,  the 
argentiferous  solution  is  separated  from  the  gold.  The  latter  is 
carefully  washed,  placed  in  a  tared  porcelain  crucible,  gently 
ignited,  and  then  weighed.  In  fine  silver  assays  the  percentage 
of  gold  is  determined  in  the  manner  indicated  on  p.  1 55. 

g.  Sulphur  (p.  279). — 1.87  grammes  of  raw  or  roasted  ore  are 
digested  for  several  hours,  in  the  cold,  with  concentrated  fuming 
nitric  acid.  An  equal  quantity  of  concentrated  hydrochloric 
acid  is  added,  and  the  liquid  heated  on  the  sand-bath,  until  the 
nitric  acid  has  been  driven  oif.  It  is  then  diluted  with  water, 
filtered,  and  the  sulphuric  acid  precipitated  with  barium  chloride. 
Or,  by  another  method,  which  is  more  easily  executed  and  gives 
sufficiently  accurate  results,  the  ore  is  fused  with  alkaline  nitrates 
and  carbonates  in  iron  dishes  under  the  muffle,  etc.  (p.  282). 

C.  SCHAFFNER'S  ASSAY  OF  ZINC  (P.  214)  AS  MODIFIED  BY 

BRUNNLECHNER.1 

Crystals  of  sodium  sulphide  are  dissolved  in  water  with  the 
application  of  heat  until  the  solution  is  supersaturated.  The 
solution  is  then  allowed  to  cool  off  and  settle.  The  clear  solution 
is  poured  off  and  diluted  with  10  to  11  times  the  quantity  by 
volume  of  water.  It  is  then  poured  into  a  flask  having  the 

1  Oesterr.  Zeitschr.  f.  Berg-,  u.  Hiittenwesen,  1879,  No.  37. 


304  APPENDIX. 

capacity  of  4  to  5  liters  and  provided  with  a  double  perforated 
cork.  Into  one  of  them  is  fitted  a  glass  siphon  with  a  rubber 
tube  and  pinch-cock,  and  into  the  other  a  short,  small,  glass  tube 
which  may  be  closed  by  a  cock  or  cork.  The  contents  of  the 
flask  are  thoroughly  shaken,  and,  the  flask  being  closed,  the  siphon 
is  filled  by  blowing  into  the  small  tube  and  opening  the  pinch- 
cock  at  the  same  time.  The  liquid  is  then  allowed  to  stand 
for  at  least  twelve  hours  before  it  is  used.  Its  strength  will  be 
diminished  within  twenty-four  hours,  to  the  extent  of  2.5  to  3- 
thousandths  by  the  oxidation  of  the  sodium  sulphide.  As  much 
chemically  pure  zinc  as  is  approximately  contained  in  the  sample 
ore  is  then  weighed  off.  If,  for  instance,  the  ore  contains  40  per 
cent,  and  0.5  gramme  have  been  weighed  off  for  the  assay,  about 
0.2  gramme  of  pure  zinc  will  be  required.  This  is  placed  in  a 
flask  capable  of  holding  half  a  liter  and  dissolved  in  10  cubic 
centimeters  of  concentrated  hydrochloric  acid.  The  solution  is 
diluted  with  100  cubic  centimeters  of  water,  and  treated  with  50 
cubic  centimeters  of  ammonia.  It  is  then  thoroughly  shaken 
and  allowed  to  stand  for  some  time,  as,  otherwise,  the  indicator 
would  be  affected  too  quickly  and  the  titer  of  the  standard  solu- 
tion would  be  too  high.  1  cubic  centimeter  of  the  solution 
should  precipitate  at  least  8,  and  at  the  utmost,  10  milligrammes 
of  zinc  from  the  assay. 

When  the  ore  contains  over  20  per  cent.,  0.5  gramme,  and,  if 
less,  1  gramme  of  zinc  carbonate  and  roasted  zinc  blende  is  dis- 
solved in  concentrated  hydrochloric  acid,  to  whicn  a  few  drops  of 
nitric  acid  have  been  added,  but  raw  zinc  blende  and  calamine 
are  dissolved  in  aqua  regia.  In  case  gelatinous  (ferruginous) 
silica  should  be  separated,  the  solution  should  be  diluted,  the 
liquid  poured  off  from  the  residue,  the  sediment  on  the  bottom 
detached  by  means  of  a  glass  rod,  again  heated  with  acid,  and 
the  two  liquids  then  united.  In  case  sulphur  should  be  separated 
from  silicious  zinc  ores,  fuming  nitric  acid  or  potassi-um  chlorate 
is  added.  -  The  solution  is  then  evaporated  to  the  consistency  of 
syrup,  in  order  to  remove  the  excess  of  acid.  The  residue  is  then 
moistened  with  a  few  drops  of  hydrochloric  acid  and  diluted  with 
20  cubic  centimeters  of  water.  To  this  are  added  30  cubic  centi- 
meters of  ammonia  and  15  cubic  centimeters  of  ammonium  car- 


SCHAFFNER'S  ASSAY  OF  ZINC.  305 

bonate.  The  solution  is  allowed  to  settle  and  then  filtered  into 
a  flask  of  500  cubic  centimeters  capacity.  The  filter  is  washed 
with  30  cubic  centimeters  of  warm  ammonia,  and  finally  with 
warm  ammoniacal  water.  When  much  ferric  hydrate  is  present 
the  precipitate  is  again  dissolved  and  precipitated  with  ammonia 
and  ammonium  carbonate.  —  Plumbi/erous  ores  :  The  assay  sample 
is  dissolved  in  nitric  acid,  and  the  solution  evaporated  with 
sulphuric  acid.  The  lead  and  calcium  sulphates  are  then  filtered 
off.  If  the  ore  contains  but  little  calcium,  it  may  be  treated  with 
nitric  acid,  and  the  lead  precipitated  with  30  cubic  centimeters 
of  ammonia,  and  15  cubic  centimeters  of  sodium  phosphate. 
When  much  calcium  is  present,  the  precipitate  is  again  dissolved 
and  precipitated. 

A  stand  with  three  shelves  is  used.  The  uppermost  shelf 
serves  for  the  reception  of  the  flask  containing  the  sodium  sulphide, 
the  second  smaller  one,  for  a  small  flask  with  a  pipette  containing 
the  indicator  solution-,  and  upon  the  lowest  shelf,  which  projects 
somewhat,  the  flask  containing  the  solution  of  zinc  is  placed. 
Over  this  hangs  a  burette  with  a  pinch-cock  fastened  to  arms  on 
the  vertical  wall,  its  mouth  being  directly  under  the  orifice  of  the 
pinch-cock  on  the  flask  containing  the  standard  solution.  Dupli- 
cate titrations  are  then  made,  between  which  only  decimal  differ- 
ences are  allowable.  Suppose  E  is  the  weight  of  the  assay  sample, 
Q  the  quantity  of  standard  solution  in  c.c.  used  for  the  precipita- 
tion, M  the  total  quantity  of  the  assay  solution  in  c.c.  ;  the  titer 
will  be  — 

T  100^ 

=  [§_(J/x  0.007)] 

if  hydrated  peroxide  of  iron  has  been  used  as  the  indicator,  or 


[§_  (If  x  0.005)] 
if  paper  saturated  with  ferric  chloride  (p.  215)  has  been  used. 

In  titrating  the  samples,  one-third  to  one-half  of  the  approxi- 
mate quantity  of  the  precipitating  agent  required  should  be  added 
every  time  to  the  solution,  and  this  well  shaken.  A  drop  of  so- 
lution of  ferric  chloride  is  added  to  the  zinc  solution  from  a  small 
pipette.  The  mass  of  hydrated  peroxide  of  iron  which  is  formed  is 
broken  up  into  as  equally  sized  flakes  of  1  to  1.5  millimeters 
20 


306  APPENDIX. 

diameter  as  possible  by  vigorously  swinging  the  flask  to  and  fro. 
This  swinging  is  constantly  continued  while  solution  of  sodium 
sulphide  is  added  by  cubic  centimeters,  until  the  color  of  the 
flakes  commences  to  change.  A  minute  is  then  allowed  for  the 
reaction  of  the  particles  of  liquid  which  have  remained  ineffective, 
and  the  precipitation  is  then  finished  by  adding  sodium  sulphide 
drop  by  drop.  If  F  is  the  quantity  of  the  precipitating  agent 
consumed  in  c.c.,  T  the  titer,  M  the  total  quantity  of  the  solu- 
tion in  c.c.  after  the  assay  is  finished,  the  percentage  of  zinc 
when  ferric  hydrate  has  been  used  as  indicator  will  be — 

^=^[^-(^"xO-007)] 


and 

Z=^\_V-(Mx  0.005)] 

when  slips  of  paper  saturated  with  ferric  chloride  have  been  used. 
When  the  first  plan  is  employed  the  titratiou  must  be  continued, 
in  order  to  ascertain  the  titer,  until  the  flakes  become  entirely 
black,  but  in  titrating  solutions  of  ore,  only  until  the  reddish- 
brown  color  has  passed  into  a  greenish  tint.  The  following  con- 
ditions are  required  for  obtaining  a  sharp  reaction :  The  flakes 
must  be  nearly  of  the  same  size,  the  flask  should  be  carefully 
swung  to  and  fro  to  prevent  the  flakes  from  being  broken  up  any 
further ;  not  too  much  of  the  precipitating  agent  must  be  added 
at  one  time,  and  it  should  not  fall  directly  upon  the  flakes,  but 
run  down  the  sides  of  the  flask ;  the  titration  should  be  done  at 
the  ordinary  temperature,  whereby  the  reaction  appears  more 
gradually  and  uniformly,  but  the  precaution  must  at  the  same 
time  be  observed  of  adding  the  standard  solution  at  longer  inter- 
vals ;  uniformity  of  quantity  and  time  in  treating  the  assays ; 
judging  the  tone  of  color  by  reflected  light ;  and  finally  the 
flake  reaction  should  be  controlled  by  a  drop  test. 

If  it  is  required  to  determine  the  amount  of  over  0.5  per  cent, 
of  lead  in  zinc  ore,  2  grammes  of  the  sample  are  dissolved  in 
nitric  acid  and  evaporated  to  dry  ness.  Some  diluted  sulphuric 
acid  is  added  to  the  dry  mass,  and  this  is  again  evaporated  until 
white  vapors  appear.  It  is  allowed  to  become  cold,  diluted  with 
20  cubic  centimeters  of  water,  filtered  and  washed  until  the  wash 


EXPERIMENTS  ON  A  HEAT-REGULATOR.  307 

water  shows  no  reaction  with  ammonium  sulphide.  The  precipi- 
tate (lead  sulphate,  calcium  sulphate,  gangue)  is  rinsed  off  into  a 
beaker  and  digested  with  a  mixture  of  ammonium  tartrate  and 
ammonia  in  excess.  The  lead  solution  is  filtered  off,  the  lead 
precipitated  with  sulphuric  acid,  and  the  lead  sulphate  dried  and 
weighed;  or,  it  is  detached  from  the  filter,  the  latter  incinerated, 
and  the  precipitate  ignited  (see  also  p.  93). 

D.  EXPERIMENTS  ON  A  HEAT-REGULATOR  AT  THE  UNITED  STATES 
ASSAY-OFFICE,  NEW  YORK.1 

Whoever  has  had  much  practical  experience  in  cupellation  must 
have  noticed  that  the  variation  of  light  depending  upon  the  clear- 
ness or  cloudiness  of  the  day  deceives  the  operator  in  his  judgment 
as  to  the  degree  of  heat  in  the  muffle.  There  is  very  perceptible 
difference  even  between  the  light  of  the  morning  and  of  the  after- 
noon during  a  perfectly  clear  day,  so  that,  if  reliance  be  placed  upon 
the  eye  alone,  as  is  now  done,  there  will  be  misjudgments  resulting 
in  very  considerable  error. 

It  often  happens  that  errors  arising  from  this  cause  are  so  serious 
as  to  necessitate  repetitions  of  the  assay,  which  would  have  been 
needless  could  the  furnace  have  been  maintained  at  the  proper  tem- 
perature. Yery  often  there  are  annoying  delays  and  embarrass- 
ments at  the  assay  office  on  this  account,  which,  in  the  old  way  of 
working,  are  unavoidable. 

With  the  purpose  of  obviating  this  difficulty,  a  pyrometer,  or, 
more  properly  speaking,  a  heat  regulator,  which  has  now  been  per- 
fected so  that  a  perfectly  uniform  temperature  may  be  automatically 
maintained  at  any  desired  degree,  has  been  designed.  By  this  appa- 
ratus the  furnace  may  be  kept  at  a  " copper,"  "silver,"  or  "gold" 
heat,  or  in  a  few  minutes  changed  from  one  to  the  other  with  perfect 
precision. 

The  value  of  such  an  appliance  to  the  bullion  assayer  is  manifest, 
and  will  at  once  be  appreciated. 

This  automatic  heat-regulator  or  pyrometer  is  based  upon  the  ex- 
pansion and  contraction  of  a  single  metallic  bar,  so  mounted  as  to 
be  independent  of  the  expansions  of  the  furnace  to  which  it  is  at- 
tached, thus  giving  a  greater  change  in  length  for  any  given  varia- 
tion of  temperature  than  those  composed  of  two  metals  whose 

1  H.  Gr.  Torrey,  Engineering  and  Mining  Journal,  August  28,  1886,  p.  147. 


308 


APPENDIX. 


co-efficients   of  expansion  are  different,  the   difference  being  the 
measuring  co-efficient. 

For  assay  furnaces,  platinum  has  been  found  to  be  the  most  suit- 
able metal,  on  account  of  its  quality  of  remaining  unoxidized  upon 
exposure  to  high  temperatures,  in  the  presence  of  currents  of  air, 
and  on  account  of  its  infusibility. 

Fig.  87. 


A  rod  A  B  (Fig.  87),  No.  12  wire  gauge,  extends  along  the  in- 
terior of  the  muffle  close  to  the  roof,  being  suspended  at  the  fore  end 
by  an  iron  bar  G  D,  about  half  an  inch  wide,  passing  freely  through 
it,  and  extending  through  the  rear  end  of  the  muffle  and  furnace. 

The  rear  end  of  the  rod  is  connected  by  a  link  to  the  centre  of  a 
short  lever  whose  fulcrum  is  at  one  end.  To  the  other  end  of  the 
lever  a  second  link  connects  with  a  second  lever  G  H,  which  serves 
to  further  magnify  the  expansion  of  the  platinum  rod.  This  second 
lever  is  extended  into  a  pointer  /,  and  has  a  total  length  of  six 
inches. 

The  levers  are  so  proportioned  that  the  extremity  of  the  pointer 
passes  through  an  arc  of  six  inches  from  a  cold  furnace  to  a  cupel- 
ling heat  for  gold  bullion  assays. 

The  pointer  plays  between  two  platinum  contacts  K  Kf,  which 
are  one-tenth  of  an  inch  apart.  These  contacts  are  electrically  con- 
nected with  an  apparatus  controlling  the  gas  supply  of  the  furnace ; 
and  the  pointer  is  also  connected  electrically  with  the  apparatus  in 


EXPERIMENTS   ON   A   HEAT-REGULATOR.  309 

such  a  manner  that,  when  it  rests  against  the  contact  nearer  the 
furnace,  it  causes  the  formation  of  a  circuit  operating  machinery 
that  opens  the  gas-cock.  When  the  pointer,  leaving  the  contact  on 
account  of  the  increased  heat,  reaches  the  other  contact,  the  opera- 
tion is  reversed. 

The  temperature  is  therefore  kept  within  the  limits  afforded  by 
the  movement  of  the  pointer  through  one-sixteenth  of  an  inch, 
which  represents  a  variation  of  temperature  of  less  than  25  degrees 
Fahrenheit. 

The  contact  points  are  fastened  to  a  rod  J  L,  which  is  pivoted 
at  its  lower  end  close  to  the  pivot  of  the  pointer.  A  rod  M  N  is 
also  pivoted  to  its  upper  end.  which  passes  to  the  front  of  the  fur- 
nace, and  is  clamped  by  a  thumb-screw  S  in  any  desired  position  to 
the  frame  that  supports  the  whole  apparatus. 

If  it  becomes  necessary  to  cool  the  furnace  for  silver  bullion 
assays,  the  operator  has  only  to  draw  the  rod  M  N  toward  him, 
thus  bringing  the  contact-bar  toward  the  zero  from  which  the 
pointer  started  when  the  furnace  was  cold.  This  movement  causes 
the  pointer  to  bear  against  the  outer  contact,  shutting  off  the  gas 
and  cooling  the  furnace  to  the  required  point,  and  no  lower. 

The  pointer  is  in.  two  sections,  pivoted  in  the  centre,  and  is  kept 
in  a  straight  line  by  a  spring  P  N,  which  allows,  without  straining 
the  apparatus,  the  deflections  that  are  made  when  the  position  of 
the  contact-bar  is  changed.  Should  the  platinum  bar  stretch,  or 
should  there  be  any  lost  motion  in  the  levers,  causing  the  pointer, 
when  the  furnace  is  cold,  to  rest  at  some  point  other  than  a  fixed 
zero,  the  error  may  be  compensated  for  by  two  nuts  that  are  placed 
one  on  each  side  of  the  supporting  bar  in  front.  The  platinum  bar 
is  kept  in  tension  by  a  spiral  spring  fastened  to  the  pointer,  and  to 
a  point  beyond  it. 

Mr.  Charles  Taylor,  of  the  U.  S.  Assay  Office  in  New  York, 
writes  under  the  date  of  April  8,  1889,  as  follows: — 

"  Since  the  above  article  appeared  in  the  Engineering  and  Mining 
Journal,  I  have  found  that  good  results  can  be  obtained  by  bolting 
the  apparatus  direct  to  the  furnace,  thus  obtaining  the  use  of  an  in- 
dependent frame.  The  index  has  also  been  simplified  so  that  but 
one  spring  is  necessary  to  take  up  the  expansion,  lost  motion,  etc., 
and  also  to  allow  for  the  deflection  of  the  index," 


310  APPENDIX. 

E.  DRY  ASSAY  OP  IRON  ORES. 

While  it  is  perfectly  true  that  the  results  obtained  by  assay- 
ing iron  ores  in  the  dry.  way  are  less  accurate  than  most  of  those 
obtained  in  the  wet  way,  on  the  other  hand  they  approximate  much 
more  nearly  to  the  economic  value  of  an  iron  ore  when  smelted  on 
a  large  scale.  The  percentage  of  metallic  iron  is  not  only  obtained, 
but  obtained  associated  or  combined  with  carbon,  phosphorus,  silica, 
sulphur,  and  manganese,  according  to  the  nature  of  the  ore,  these 
elements  being  present  relatively  in  about  the  same  proportions  as 
when  the  ore  is  smelted  in  a  blast  furnace.  The  assay  consequently 
gives  a  very  fair  and  accurate  idea  of  what  may  be  expected  of 
any  particular  iron  ore  in  a  blast  furnace,  not  only  as  regards  the 
yield  of  iron,  but  also  the  composition  and  action  of  the  fluxes. 
From  a  few  systematic  assays  one  is  not  only  enabled  to  form  a 
good  idea  of  the  quality  of  the  iron  which  would  be  produced  on 
a  large  scale,  but  the  fluxes  giving  the  best  results  with  the  ore 
can  readily  be  determined.  This  cannot  always  be  done  on  the 
basis  of  a  chemical  analysis  alone,  no  matter  how  complete  and  ac- 
curate it  may  be.  It  will  therefore  be  observed  that  this  system  of 
dry  assays  particularly  commends  itself  for  use  with  new  and  un- 
tried ores.  It  is  usually  best  to  make  a  preliminary  assay  in  the 
wet  way  in  order  to  determine  the  earthy  matter  present.  Berthier 
recommends  the  following  process  :l — 

A  weighed  quantity  of  the  finely  powdered  ore  is  heated  to  red- 
ness in  a  porcelain  crucible ;  the  loss  of  weight  gives  the  amount  of 
water,  carbonic  acid,  and  other  volatile  matters  present.  Another 
weighed  portion  is  heated  with  dilute  nitric  acid,  which  dissolves 
out  carbonates  of  lime  and  magnesium  ;  the  residue  contains,  under 
ordinary  circumstances,  only  oxide  of  iron,  clay,  and  quartz,  the 
difference  giving  the  amount  of  the  earthy  carbonates.  A  third 
portion  is  treated  with  strong  hydrochloric  acid,  whereby  the  car- 
bonates of  lime  and  magnesium,  and  the  oxides  of  iron  ore  dissolved 
out,  leaving  an  insoluble  residue  of  quartz  and  clay.  This  is 
weighed,  the  oxides  of  iron  being  determined  from  the  difference  of 
weight  by  deducting  that  of  the  carbonates  previously  found.  From 
these  results  the  proportion  of  fluxes  necessary  to  be  added  can  be 
approximately  determined  with  a  view  to  produce  an  easily  fusible 
slag.  In  many  instances,  however,  this  preliminary  assay  can  be 
dispensed  with,  as  a  sufficiently  good  idea  of  the  nature  of  the  fluxes 

1  Metallurgy  of  Iron.     H.  Bauerman.     London,  1882,  p.  104. 


DRY  ASSAY  OF  IRON  ORES.  311 

to  be  added  can  be  determined  by  the  appearance  of  the  ore  alone. 
The  dry  assay  of  iron  may  be  performed  either  in  plain  clay  cruci- 
bles, or,  preferably,  in  basqued,  or  charcoal  lined  crucibles  or  some 
other  carbonaceous  material.  In  the  former  case  the  ore  must  be 
mixed  with  from  20  to  30  per  cent,  of  powdered  charcoal. 

The  basqued  crucibles  are  prepared  as  follows:1  The  charcoal 
powder  is  mixed  with  just  sufficient  gum-water  or  molasses  to  make 
it  cohere  readily.  The  crucible  is  gently  rammed  full  of  this  char- 
coal, and  a  cylindrical  cavity  of  sufficient  size  to  contain  the  charge  is 
made  in  it  with  a  spatula  or  some  other  kind  of  boring  instrument. 

The  crucibles  best  adapted  for  this  assay  are  made  of  a  mixture  com- 
posed of  two  parts  unburnt  and  one  of  burnt  clay.  They  are  about  If 
inches  high  and  1 J  inches  in  diameter  at  the  top.  As  the  amount  of 
ore  in  the  charges  never  exceeds  from  10  to  15  grains  (0.64  to  0.96 
grammes),  four  crucibles  are  placed  in  the  furnace  at  a  time.  The 
charges  in  each  are  exactly  alike,  and  if  there  is  but  a  slight  varia- 
tion in  the  weight  of  the  resulting  button,  the  assay  is  probably 
correct ;  the  mean  weight  of  the  four  should  be  taken 
as  the  result.2  It  is  generally  best  to  stand  or  lute  FiS-  86- 
the  four  crucibles  to  a  half  brick,  so  that  when  the 
fusion  is  finished  all  the  crucibles  can  be  removed 
from  the  furnace  at  one  time.  Although  lids  are 
sometimes  used  to  cover  the  crucibles  it  is  better; 
after  the  charge  has  been  introduced,  to  stop  the 
cavity  with  a  charcoal  plug  and  to  cover  the  en- 
tire top  of  the  crucible  with  a  clay  luting  as  shown  c.  Cavity  contain- 
in  Fig.  86.  ing  charge- 

The   half  brick   holding  the  crucibles  should  be    Lt  Clay  iutmg. 
placed   near  or   directly  upon   the  fire   bars  at  the 
bottom  of  the   furnace,  and  the  anthracite  or  coke  fire  built  up 
around  and  over  them.     When  the  crucibles  have  been  in  the  fire 
about  li  to  2  hours,  and  a  white  heat  reached  and  maintained 
through  a  considerable  part  of  this  period,  the  assay  may  be  con- 
sidered finished  and  the  crucibles  removed.     When  the  crucibles  are 
cold  they  are  broken  up,  the  metallic  buttons  and  globules3  which  may 
adhere  to  the  charcoal  lining  and  slag  are  separated  out  with  a  magnet. 

1  Percy's  Metallurgy.     Fuel.     London,  1875,  p.  140. 

2  With  the  same  ore  the  variation  between  the  buttons  should  not  be  over 
a  few  tenths  per  cent. 

3  The  formation  of  these  globules  is  prevented  by  not  allowing  any  fine  par- 
ticles of  charcoal  or  dirt  to  get  into  the  cavity  when  it  is  being  charged. 


312  APPENDIX. 

After  weighing,  the  buttons  should  be  fractured  and  the  character  of 
the  iron  carefully  noted.  The  character  of  the  slag  must  likewise  be 
carefully  observed.  •  If  there  is  too  much  silica  in  the  flux  it  has  a 
greenish  tint  and  is  transparent ;  if  translucent,  blue  or  grayish 
enamel,  lime,  clay,  and  silica  are  in  the  proper  proportions  ;  if  rough, 
stony,  or  crystalline,  it  is  too  basic  and  has  a  dull  lustre.  Should 
the  charge  be  fritted,  pulverulent,  and  the  iron  diffused  in  minute 
particles,  the  flux  has  been  wrongly  proportioned,  or  the  temperature 
too  low.  This  is  apt  to  happen  with  ores  containing  a  large  pro- 
portion of  lime  and  magnesium,  as  they  are  always  refractory  and 
require  the  addition  of  a  large  proportion  of  silica  and  lime.  If  the 
slag  is  but  half  fused  and  dark  in  color,  the  ore  contains  an  excess 
of  silica  or  silicates  of  iron  and  manganese,  which  react  on  the 
carburetted  iron,  decomposing  it,  forming  malleable  iron  and  car- 
bonic acid,  which  escapes  through  the  slag,  giving  it  a  spongy  ap- 
pearance. In  this  case  lime  should  be  added.  The  presence  of  a 
small  amount  of  manganese  is  indicated  by  the  amethystine  color  of 
the  slag ;  larger  amounts  render  it  olive  green,  yellowish,  or  brown. 

Titaniferous  ores  are  apt  to  render  the  slag  copper-colored  by  the 
formation  of  cyano-nitride  of  titanium.  They  may  also  be  black 
and  hard,  or  else  bluish  and  vitreous.  Chromic  iron  ores  produce  a 
resinous  and  dark-colored  slag,  which  is  sometimes  surrounded  with 
a  thin  metallic  layer.  As  a  general  thing  the  iron  buttons  are  dark- 
gray  or  mottled,  according  to  the  condition  and  amount  of  carbon 
they  contain.  If  the  crucibles  are  allowed  to  cool  very  slowly,  the 
buttons  are,  as  a  rule,  very  graphitic,  but  if  cooled  quickly  are 
fine-grained  and  white,  or  grayish  in  color.  If  the  ores  are  easily 
reducible,  and  the  proper  temperature  has  been  reached  and  main- 
tained in  the  furnace,  the  buttons  should  be  dark,  tough,  and,  if 
they  have  not  been  cooled  too  quickly,  graphitic. 

The  presence  of  phosphorus  generally  renders  the  buttons  white, 
hard,  and  brittle ;  sulphur  produces  a  mottled  or  reticulated  struc- 
ture ;  manganese  a  hard,  white,  crystalline  or  close-grained  iron  ; 
titanium  a  dull  dark-gray  button  with  a  crystalline  fracture; 
chromium  a  well-fused  button,  with  a  tin-white,  bright  crystalline 
fracture,  to  a  semi-fused  white,  or  light-gray,  spongy  mass,  accord- 
ing to  the  amount  of  chromium  in  the  iron.1 

Proportion  of  fluxes. — The  fluxes  should  be  so  adjusted  as  to 
obtain  a  well-fused  clean  slag,  in  sufficient  quantity  to  completely 

1  Percy's  Metallurgy.     Iron  and  Steel.     London,  1864.     p.  243. 


DRY   ASSAY  OF   IRON  ORES.  313 

cover  the  reduced  button  of  metal.  Blast  furnace  slags  of  the  fol- 
lowing composition  may  be  taken  as  types  of  the  slags  most  de- 
sirable : — 

CaO.Si02+  Al203.3Si02  =  lime  30,  alumina  14,  silica  56  per 
cent. 

2(2CaO.Si02)  -f  2Al2O3.3Si02  =  lime  41,  alumina  15,  silica  37 
per  cent.1 

If  the  composition  of  the  ore  is  approximately  known,  the  amount 
of  fluxes  necessary  to  produce  a  fusible  slag  can  be  easily  ascer- 
tained. When  necessary  an  extra  amount  of  flux  must  be  added 
in  order  to  produce  sufficient  slag  to  cover  the  button. 

As  a  rule  the  following  fluxes  will  be  found  best  adapted  to  ores 
or  metallurgical  products,  which  would  be  classed  under  the  follow- 
ing several  general  heads.  The  proportions  given  are  for  10 
grains  (0.65  gramme)  of  ore  :2 — 

1.  Ores  nearly  free  from  gangue,  some  varieties  of  magnetite, 
red  and  brown  hematite,  specular  iron  ore,  and  micaceous  iron 
ore : — 


Parts. 


China  clay   ...     2 
Lime        ....     2^ 
Sand  .  ,     0-1 


Parts. 


Glass      ....     2-2$ 
Lime      ....     2$-3 


Parts. 


Blast-furnace  slag      5 
Fluor  spar    ...     5 


2.  Ores,  etc.,  containing  silica,   varieties  of  limonite  or  brown 
iron  ore,  refinery  slag  (tap),  and  flue  cinders : — 


Parts. 


Glass 1-2$ 

Lime 2$-4 


Parts. 


China  clay 2 

Lime 3$-4 


3.  Ores,  containing  carbonates  of  lime,  magnesia,  protoxide  of 
manganese,  etc.,  calcareous  hematites,  and  spathic  ores  :  — 


Parts. 

China  clay 2 

Lime 1$ 

Sand  1 


Parts. 

Glass     .........  3-4 

Lime 


4.  Ores  containing  silica  and  alumina,  clay  iron  ores,  etc. : — 


Parts. 


Glass 0-2$ 

Lime 2$-3 


Parts. 


China  clay 0-2 

Lime  .  2-3 


1  Metallurgy  of  Iron.     H.  Bauerman.     London,  1882.     p.  105. 

2  A  universal  flux  known  as  Percy's  slag,  lime  3,  silica  2$,  and  clay  1  part, 
is  sometimes  used.     School  of  Mines  Quarterly.     Vol.  II.,  p.  173. 


314  APPENDIX. 

5.  Titaniferous  ores,  or  ores  containing  titanium  i1 — 


Parts. 
....      3 

China  clay   . 

Parts. 
.      .      2 

Glass  

Glass 

2 

Lime  • 

Lime 

China  clay    .     .     . 

Parts. 


1 

The  ores  should  be  powdered  and  passed  through  an  80  mesh 
sieve  (80  meshes  per  linear  inch, — 2J  centimeters).  The  use  of 
iron  mortars  should  be  avoided.  When  necessary  the  ore  should 
be  dried  at  about  110°  C.  Some  ores  contain  hydroscopic  as  well 
as  combined  water. 

Fluxes. — Silica  in  the  form  of  white  quartz  or  rock  crystal, 
finely  pulverized,  is  preferred  on  account  of  its  purity  ;  but  white 
sand  used  in  glass-making  forms  a  good  substitute. 

Glass,  such  as  plate,  crown,  or  window,  finely  pulverized,  is  used. 
It  contains  from  60  to  70  per  cent,  silica,  and,  being  fusible,  forms 
a  good  substitute  for  silica  or  silicates  of  alumina.  Green  glass 
containing  oxide  of  iron,  or  flint  glass  containing  lead,  is  objec- 
tionable. 

China  clay,  or  the  hydrated  silicate  of  alumina,  forms  a  very 
pure  and  useful  flux,  as  it  is  practically  free  from  oxide  of  iron.  It 
is  either  used  in  a  hydrated  or  dehydrated  state.  In  the  latter  case 
it  is  pulverized  and  heated  to  redness. 

Lime. — The  common  powdered,  unslacked  lime  should  be  used  ; 
limestone,  chalk,  or  any  varieties  of  carbonate  of  lime  are  good 
substitutes.  Care  must  be  taken  that  the  lime  flux  is  free  from 
sulphates. 

Assay  in  large  unlined  crucibles. — It  is  very  good  practice,  and 
at  the  same  time  shows  how  an  iron  assay  can  be  made  in  an  un- 
basqued  crucible,  to  make  a  series  of  assays  to  show  the  effect  of 
too  little,  the  proper  amount,  and  too  much  carbon  on  the  result. 

The  fluxes  and  ore  should  be  pulverized  and  passed  through  a 
60  mesh  sieve.  With  a  series  of  four,  the  ore  and  fluxes  may  be 
proportioned  as  follows : — 


1  and  2. 


Ore  .  .  .  500  grains  (32  grammes) 
Glass  .  .  250  "  (16  "  ) 
Lime  .  .  300  "  (19.2  "  ) 


3  and  4. 


Ore    .     .     .  500  grains  (32  grammes) 

China  clay  200      "      (12.8     "       ) 

Sand      .     .  50       "      (  3.2     "        ) 

Lime      .     .  250      "      (16        "       ) 


1  This  assay  requires  the  highest  possible  temperature  that  can  be  obtained 
in  an  ordinary  furnace,  and  to  be  subjected  to  such  a  temperature  a  somewhat 
longer  time  than  usual. 


DRY  ASSAY  OF  IRON   ORES.  315 

The  reducing  agent  employed  is  preferably  anthracite,  but  char- 
coal or  coke  may  be  used.  In  any  case  it  should  be  pulverized  and 
passed  through  a  60  mesh  sieve.  The  following  amounts  are  re- 
spectively used  : — 


1.  80  grains  (5.12  grammes) 

2.  110      "      (7.04        "       ) 


3.  120  grains  (7.68  grammes) 

4.  150      "      (9.60        "       ) 


Mix  the  fluxes  and  reducing  agent  thoroughly  with  the  ore, 
transfer  to  a  crucible  about  4  inches  high  by  1J  inches  in  diameter 
(10.12  by  3.19  centimeters).  Lute  cover  on  with  clay,  place  on 
piece  of  fire-brick  and  heat  in  usual  manner  for  an  hour  or  more. 
In  lifting  the  crucible  out  of  the  furnace,  care  must  be  taken  to 
shake  it  as  little  as  possible  in  order  to  avoid  disseminating  globules 
of  iron  in  the  slag.  When  cold  break  open  the  crucible,  and  collect 
any  small  buttons  or  shots  of  metals  in  the  slag  with  a  magnet. 
Weigh,  then  fracture  the  largest  button  and  note  the  character  of 
the  iron.  If  the  above  scheme  has  been  carefully  carried  out,  using 
an  ordinary  hematite  or  magnetic  ore,  the  results  will  be  something 
like  as  follows : — 

1.  Not  being  sufficient  carbon  present  the  ore  is  not  all  reduced  ; 
the  reduced  and  unreduced  ore  being  fritted  together  with  slag  in 
an  irregular  lump. 

2.  Ore  completely  reduced  and  fused  into  a  button.     Iron,  gray. 
Slag,  glassy,  and  transparent,  or  perhaps  dark-grayish,  and  opaque. 

3.  Ore  completely  reduced  and  fused  into  a  well-melted  button. 
Iron,  gray  to  grayish-white.     Slag,  clear,  glassy,  and  transparent, 
color,  gray  to  greenish  by  transmitted  light. 

4.  Ore  completely  reduced,  but  owing  to  the  excess  of  carbon 
present  the  metal  is  disseminated  through  the  slag  in  small  shots 
or  globules.     Iron,  gray.     Slag,  glassy,  opaque,  or  translucent. 

There  should  always  be  present  an  excess  of  the  amount  of  carbon 
necessary  to  reduce  the  ore.  100  parts  by  weight  of  sesquioxide  of 
iron  require  22^  parts  of  carbon  for  reduction.  Consequently  the 
amount  added  must  be  adjusted  according  to  the  oxide  of  iron 
present.1 

1  Percy's  Metallurgy.     Iron  and  Steel,     p.  243. 


THE 

METRIC  SYSTEM  OF  WEIGHTS  AND  MEASURES. 


THE  United  States  being  the  first  to  introduce  the  decimal 
system  into  the  coinage  of  the  country,  and  to  demonstrate  its 
superior  utility,  it  is  remarkable  that  we  have  hesitated  so  long 
in  regard  to  the  substitution  of  the  same  simple  and  rational 
system  of  weights  and  measures  for  the  complicated  and  con- 
fused standards  in  general  use. 

In  May,  1866,  the  Committee  on  Coinage,  Weights,  and  Mea- 
sures presented  to  the  House  of  Representatives  an  exhaustive 
report,  accompanied  by  bills  authorizing  the  introduction  of 
the  metric  system  into  the  various  departments  of  trade,  and 
making  all  contracts,  based  on  this  system  of  weights  and 
measures,  valid  before  any  court  in  the  United  States.  They 
said : — 

"THE  METRIC  SYSTEM. 

"  It  is  orderly,  simple,  and  perfectly  harmonious,  having  use- 
ful relations  between  all  its  parts.  It  is  based  on  the  METEK, 
which  is  the  principal  and  only  arbitrary  unit.  The  meter  is  a 
measure  of  length,  and  was  intended  to  be,  and  is,  very  nearly 
one  ten-millionth  of  the  distance  on  the  earth's  surface  from 
the  equator  to  the  pole.  It  is  39.37  inches,  very  nearly. 

'The  are  is  A  surface  equal  to  a  square  whose  side  is  10 
meters.  It  is  nearly  four  square  rods. 

"  The  liter  is  the  unit  for  measuring  capacity,  and  is  equal  to 
the  contents  of  a  cube  whose  edge  is  a  tenth  part  of  the  meter. 
It  is  a  little  more  than  a  wine  quart. 

"The  gramme  is  the  unit  of  weight,  and  is  the  weight  of  a 
cube  of  water,  each  edge  of  the  cube  being  one  one-hundredth 
of  the  meter.  It  is  equal  to  15.432  grains. 

"  The  stere  is  the  cubic  meter. 

"Each  of  these  units  is  divided  decimally,  and  larger  units 
are  formed  by  multiples  of  10,  100,  &c.  The  successive  mul- 
tiples are  designated  by  the  prefixes,  dtka,  hecto,  kilo,  and  ntyria  ; 
the  subordinate  parts  by  deci,  centi,  and  milli,  each  having  its 
own  numerical  significance. 

"The  nomenclature,  simple  as  it  is  in  theory,  and  designed 

1  317 


318  THE    METRIC    SYSTEM. 

from  its  origin  to  be  universal,  can  only  become  familiar  by 
use.  Like  all  strange  words,  these  will  become  familiar  by 
custom,  and  obtain  popular  abbreviations.  A  system  which 
has  incorporated  with  itself  so  many  different  series  of  weights, 
and  such  a  nomenclature  as  'scruples,'  'pennyweights,'  'avoir- 
dupois,' and  with,  no  invariable  component  word,  can  hardly 
protest  against  a  nomenclature  whose  leading  characteristic  is  a 
\short  component  word  with  a  prefix  signifying  number.  We 
are  all  familiar  with  thermometer,  barometer,  diameter,  gasometer, 
&c..  with  telegram,  monogram,  &c.,  words  formed  in  the  same 
manner. 

"After  considering  every  argument  for  a  change  of  nomen- 
clature, your  committee  have  come  to  the  conclusion  that  any 
attempt  to  conform  it  to  that  in  present  use  would  lead  to  con- 
fusion of  weights  and  measures,  would  violate  the  early  learned 
order  and  simplicity  of  metric  denomination,  and  would  seri- 
ously interfere  with  that  universality  of  system  so  essential  to 
international  and  commercial  convenience. 

"When  it  is  remembered  that  of  the  value  of  our  exports 
and  imports,intheyearending  June  30, 1860,  in  all  $762,000,000, 
the  amount  of  near  $700,000,000  was  with  nations  and  their  de- 
pendencies that  have  now  authorized,  or  taken  the  preliminary 
steps  to  authorize,  the  metric  system,  even  denominational  uni- 
formity for  the  use  of  accountants  in  such  vast  transactions 
assumes  an  important  significance.  In  words  of  such  universal 
employment,  each  word  should  represent  the  identical  thing  in- 
tended, and  no  other,  and  the  law  of  association  familiarizes  it. 

"Your  committee  unanimously  recommend  the  passage  of 

the  bills  and  joint  resolutions  appended  to  this  report 

The  metric  system  is  already  used  in  some  arts  and  trades  in 
this  country,  and  is  especially  adapted  to  the  wants  of  others. 
Some  of  its  measures  are  already  manufactured  at  Bangor,  in 
Maine,  to  meet  an  existing  demand  at  home  and  abroad.  The 
manufacturers  of  the  well-known  Fairbanks'  scales  state:  'For 
many  years  we  have  had  a  large  export  demand  for  our  scales 
with  French  weights,  and  the  demand  and  sale  are  constantly 
increasing.'  Its  minute  and  exact  divisions  specially  adapt  it 
to  the  use  of  chemists,  apothecaries,  the  finer  operations  of  the 
artisan  and  to  all  scientific  objects.  It  has  always  been  and  is 
now  used  in  the  United  States  coast  survey,  Yet  in  some  of 
the  States,  owing  to  the  phraseology  of  their  laws,  it  would  be 
a  direct  violation  of  them  to  use  it  in  the  business  transactions  of 
the  community.  It  is,  therefore,  very  important  to  legalize  its  use, 
and  to  give  to  the  people,  or  that  portion  of  them  desiring  it,  the 
opportunity  lor  its  legal  employment,  while  the  knowledge  of 
its  characteristics  will  be  thus  diffused  among  men." 

2 


WEIGHTS    AND    MEASURES.  319 

WEIGHTS  AND  MEASURES. 
APOTHECARIES'  WEIGHT,  U.  S. 

Pound.  Ounces.  Drachms.  Scruples.  Grains. 

Ibl    =    12   —   90    =   288  =  5760 

§  1    =    8   =    24  =  480 

31=     3  =  60 

B  1  =  gr.  20 

The  imperial  standard  Troy  weight,  at  present  recognized  by  the  British 
hiws,  corresponds  with  the  apothecaries'  weight  in  pounds,  ounces,  and 
grains,  but  differs  from  it  in  the  division  of  the  ounce,  which,  according  to 
the  former  scale,  contains  twenty  pennyweights,  each  weighing  twenty- 
four  grains. 

AVOIRDUPOIS  WEIGHT. 

Pound.  Ounces.  Drachms.  Troy  grains. 

It)  1    =    16    =    256    =   7000. 
oz.  1    =    16    =    437.5 

dr.  1    =     27.34375 

Relative  Value  of  Troy  and  Avoirdupois  Weights. 

Pound.  Pounds.  Pound.      Oz.         Grains. 

1  Troy  =    0.822857  Avoirdupois  =     0         13         72.5 

1  Avoirdupois  =     1.215277  Troy  =1  2       280. 

WINE  MEASURE,  U.  S. 

Gallon.        Pints.    Fluidounces.     Fluidrachms.       Minims.     Cubic  inches. 

Cong.  1     =     8    =    128      =       1024  ==  61440  =  231. 

0 1     =       16      =        128  =      7680  =     28.875 

f§    1      =  8  =        480  =      1.8047 

f5  1  =  n  GO  =      0.2256 

IMPERIAL  MEASURE. 

Adopted  by  all  the  British  College. 
Gallon.  Pints.        FJuidounces.      Fluidrachms.  Minims. 

1       =      8      =      160        =      1280  =  76800 

1      =        20        =        160  =  9600 

1        =            8  =  480 

1  =  60 

Relative  Value  of  Apothecaries''  and  Imperial  Measures. 
APOTHECARIES'  MEASURE.  IMPERIAL  MEASURE. 

Pints.        Fluidozs.       Fluidrms.        Minims. 

Igallcn          =  6            13               2  23 

1  pint              =  16                5  18 

1  fluidounce   =  1                0  20 

1  fluidrachm  =  1  2.5 

1  minim          ==  1.04 

IMPERIAL  MEASURE.  APOTHECARIES'  MEASURE. 

Gallon.     Pints.     Fluidoz.     Fluidrms.  Minims 

1  gallon          =  119  58 

Ipint  =  1  3  1          38 

1  fluidounce   =  7          41 

1  fluidrachm  =  58 

1  minim          =  0.96 


320  WEIGHTS   AND   MEASURES. 

Relative  Value  of  Weights  and  Measures  in  Distilled  Water  at  60°  Fahr. 

1.  Value  of  Apothecaries'  Weight  in  Apothecaries'  Measure. 

Pints.      Flnidoz.     Fluidr.        Minims. 

1  pound  =  0.7900031  pints              =0            13            5  7.2238 

1  ounce  ==  1.0533376  fluidounces   =0              1            0  25.6020 

1  drachm  =  1:0533376  fluidrachms  =    001  3.2002 

1  scruple  =  000  21.0667 

1  grain  =  000  1.0533 

2.  Value  of  Apothecaries'  Measure  in  Apothecaries'  Weight. 

Pounds.   Oz.  Dr.  Sc.       Gr.  Grains. 

1  gallon          =  10.12654270  pounds  =  10    1     4    0  8.88  =  58328.886 

1  pint              =    1.26581783  pounds  =1311  11.11  =    7291.1107 

I  fluidounce   =    0.94936332  ounces  =    0    0    7    1  15.69=      455.6944 

1  fluidrachm  =    0.94936332  drms.     =0002  16.96  =       56.9618 

1  minim          =    0.94936332  grains    =  1.9493 

3.  Value  of  Avoirdupois  Weight  in  Apothecaries'  Measure. 

Pints.   Fluidozs.   Fluidrms.     Minims. 

1  pound  =    0.9600732  pints  =0  15          2  53.3622 

1  ounce  =    0.9600732  fluidounces    =0  07  40.8351 

4.  Value  of  Apothecaries'  Measure  in  Avoirdupois  Weight. 

1  gallon          =     8.33269800  pounds. 
1  pint  =    1.04158725  pounds. 

1  fluidounce   =    1.04158725  ounces. 

5.  Value  of  Imperial  Measure  in  Apothecaries'  and  Avoirdupois  Weights. 

Imperial  Measure.    Apothecaries'  "Weight.    Avoirdupois  Weight.  Grains.     Cubic  inches. 

1  gallon          =  12  R>  1  §  65  2  B  0  gr.  =  10 ft  0 §  =70,000      =277.27384 
1  pint  =161      2    10       =14=  8,750      =  34.65923 

1  fluidounce   =  7      0    17.5    =  1     =      4S7.5  =     1.73296 

1  fluidrachm  =  2    14.69  =  54.69=    0.21662 

1  minim          =  0.91=    0.00361 

In  converting  the  weights  of  liquids  heavier  or  lighter  than  water  into 
measures,  or  conversely,  a  correction  must  be  made  for  specific  gravity.  In 
converting  weights  into  measures,  the  calculator  may  proceed  asif  the  liquid 
was  water,  and  the  obtained  measure  will  be  the  true  measure  inversely  as 
the  specific  gravity.  In  the  converse  operation,  of  turning  measures  into 
weights,  the  same  assumption  may  be  made,  and  the  obtained  weight  will 
be  the  true  weight  directly  as  the  specific  gravity. 

4 


TABLES 

SHOWING  THE 

RELATIVE  VALUES  OP  FRENCH  AND  ENGLISH  WEIGHTS 
AND  MEASURES,  &c. 


Measures  of  Length. 

Millimetre  —         0.03937  inch. 

Centimetre  =         0.393708         " 

Decimetre  =          3.937079  inches. 

Metre  =       39.37079  " 

«  =          3.2808992  feet. 

«  =          1.093633  yard. 

Decametre  =        32.808992  feet. 

Hectometre  =      328.08992  " 

Kilometre  =    3280.8992  « 

"  =    1093.633  yards. 

Myriametre  =  10936.33  " 

«  =          6.2138  miles. 

2.539954  centimetres. 

3.0479449  decimetres. 
0.91438348  metre. 
1.82876696     " 

5.029109  metres. 
201.16437  " 

1609.3149  " 

1852  « 

321 


Inch  (¥V  yard) 
Foot  (i  yard) 
Yard 

Fathom  (2  yards) 
Pole  or  perch  (5£  yards) 
Furlong  (220  yards) 
Mile  (1760  yards) 
Nautical  mile 
21 


322         VALUES   OF  FRENCH  AND  ENGLISH 


Superficial  Measures. 

Square  millimetre  =  ^         square  inch. 


centimetre  * 

decimetre 
it 

metre  or  centiare 


Are 


Hectare  = 

Square  inch  = 

«  U  — 

"       foot  = 

"       yard  = 

"       rod  or  perch  = 

Rood  (1210  sq.  yards)  = 

Acre  (4840  sq.  yards)  = 


0.00155 

0.155006        "         " 
15.50059         "      inches. 

0.107643       "      foot. 

1550.05989         "      inches. 

10.764299        "      feet. 

1.1 9 £033       "      yard 

1076.4299  "      feet. 

119.6033  "      yards. 

0.098845  rood. 
11960.3326      square  yards. 

2.471143  acres. 

645.109201  square  millimetres, 
6.451367        "      centimetres 
9.289968        "      decimetres. 
0.836097        "      metre. 
25.291939       "      metres. 
10.116775  ares. 
0.404671  hectare. 


Measures  of  Capacity. 

Cul>ic  millimetre  =      0.000061027  cubic  inch. 

"      centimetre  or  millilitre    = 


10      "  centimetres  or  centilitre  = 

100    "  "            "  decilitre    = 

1000  *'  "             "  litre           = 

it       te  it                 tt  tt 


0.061027 

0.61027  "       " 

6.102705  "   inches. 

61.0270515          " 
1.760773        imp'l  pint. 
'     "  "  "     **  =      0.2200967          "      gal'n. 

Decalitre  =  610.270515  cubic  inches. 

"  =      2.2009668  imp.  gal'ns. 

Hectolitre  =      3.531658  cubic  feet. 

"  =    22.009668  imp.  gal'ns. 

Cubic  metre  or  stere  or  kilolitre  =      1.30802  cubic  yard. 


Myrialitre 


35.3165807 
353.105807 


"   feet. 

M     *: 


WEIGHTS  AND   MEASURES,    ETC. 


Cubic  inch. 
"      foot 
"      yard 


16.386176         cubic  centimetres. 
28.315312  "      decimetres. 

0.764513422      "     metre. 


American  Measures. 

Winchester  or  U.S.  gallon  (231  cub. in.)        =        3.785209  litres. 

"     bushel(2150.42cub.in.)  =      35.23719       " 
Chaldron  (57.25  cubic  feet)  =  1621.085  " 

British  Imperial  Measures. 

Gill  =    0.141983  litre. 

Pint  Q  gallon)  =    0.567932 

Quart  (£  gallon)  =    1.135864  " 
Imperial  gallon  (277.2738  cub.  in.)  =    4.54345797  litres. 

Pe.;k  (2  gallons)  =    9.0869159  " 

Bushel  (8  gallons)  =  36.347664  « 

Sack  (3  bushels)  =    1.09043  hectolitre. 

Quarter  (8  bushels)  =    2.907813  hectolitres. 

Chaldron  (12  sacks)  =13.08516  " 


Milligramme 


Weights. 

0.015438395  troy  grain. 


Centigramme 

= 

0.15438395 

«         n 

Decigramme 

= 

1.5438395 

«         « 

Gramme 

= 

15.438395 

"     grains. 

ii 

= 

0.643 

pennyweight. 

« 

= 

0.0321633 

oz.  troy. 

« 

= 

0.0352889 

oz.  avoirdupois. 

Decagramme 

= 

154.38395 

troy  grains. 

14 

= 

5.64 

drachms  avoirdupois. 

Hectogramme 

= 

3.21633 

oz.  troy. 

M 

= 

3.52889 

oz.  avoirdupois. 

Kilogramme 

= 

2.6803 

Ibs.  troy. 

« 

= 

2.205486 

11)8.  avoirdupois. 

Myriagramme 

= 

26.803 

Ibs.  troy. 

« 

= 

22.05486 

Ibs.  avoirdupois. 

Quintal  metrique  =    100  kilog.  =    220.5486  Ibs.  avoirdupois. 
Tonne  =  1000  kilog.  =  2205.486      "  " 


324     VALUES  OF  FRENCH  AND  ENGLISH 

Different  authors  give  the  following  values  for  the  gramme  : — 
Gramme  =  15.44402     troy  grains. 
"  =  15.44242 

"  =  15.4402  " 

"  ==  15.433159  " 

"          =  15.43234874      " 

AVOIRDUPOIS. 

Long  ton  =  20  cwt.  =  2240  Ibs.  ==  1015.649  kilogrammes. 

Short  ton  (2000  Ibs.)  =  906.8296  " 

Hundredweight  (112  Ibs.)  =      50.78245 

Quarter  (28  Ibs.)  =      12.6956144 

Pound  ==  16  oz.  =  7000  grs.  =  453.4148  grammes. 

Ounce  =  16  dr'ms.  =  437.5  grs.  =      28.3375  " 

Drachm  =.  27.344  grains  =        1.77108  gramme. 

TROY  (PRECIOUS  METALS). 

Pound  =  12  oz.  =  5760  grs.  =  373.096  grammes. 

Ounce  =  20  dwt.  —  480  grs.  =      31.0913  " 

Pennyweight  =  24  grs.  t=        1.55457  gramme. 

Grain  =        0.064773  " 

APOTHECARIES'  (PHARMACY). 

Ounce  =  8  drachms  =  480  grs.    =      31.0913        gramme. 
Drachm  =  3  scruples  =  60  grs.    =        3.8869  " 

Scruple  =  20  grs.  =        1.29546      gramme. 

CARAT  WEIGHT  FOR  DIAMONDS. 

1  carat  =  4  carat  grains  =  64  carat  parts. 
"         =  3.2      troy  grains. 
"        =  3.273   "        " 

==  0.207264  gramme 
=  0.212  " 

"        =  0.205  " 

Great  diversity  in  value. 
8 


WEIGHTS  AND   MEASUEES,    ETC.  325 

Proposed  Symbols  for  Abbreviations. 


M  —  myria  — 

10000 

Mm 

Mg 

Ml 

K—  kilo      — 

1000 

Km 

Kg 

Kl 

H  —  hecto   — 

100 

Hm 

Hg 

HI 

Ha 

D—  deca     — 

10 

Din 

Dg 

Dl 

Da 

Unit 

1 

metre  —  in 

gramme  —  g 

litre—  1 

are  —  a 

a—  deci       — 

0.1 

dm 

dg 

dl 

da 

o  —  centi     — 

0.01 

cm 

eg 

cl 

ca 

m  —  milli    — 

0.001 

mm 

ing 

ml 

Km  =  Kilometre.  HI  =  Hectolitre.  eg  =  centigramme, 
c.  cm  =  cm3  =  cubic  centimetre,  dm2  =  sq.  dm  =  square  deci- 
metre. Kgm  =  Kilogrammetre.  Kg0  =  Kilogramme  degree. 


Celsius  or  Centigrade. 


Fahrenheit. 


Reaumur. 


—  15° 

4    5° 

—  12° 

—  10 

h  I4 

—     8 

—     5 

-  23 

—    4 

0  melting 

-  32 

ice          0 

-     5 

-  41 

4-    4 

r  10 

-  50 

4-    8 

-  15 

-  59 

4-  12 

-  20 

-  68 

4-  16 

-  25 

-  77 

4  20 

h  30 

4  86 

4-  24 

-  35 

4  95 

4  28 

-  40 

4104 

h  32 

h  45 

4113 

-  36 

4-  50 

4122 

-  40 

4-  55 

4131 

-  44 

4-  60 

4140 

-t-  48 

4  65 

4149 

4-  52 

4-  TO 

-158 

+  56 

4  75 

-167 

4-  60 

4-  80 

-176 

h  64 

-f  85 

-185 

-  68 

4-  90 

4194 

-  72 

4  95 

4-203 

-  76 

4-  100  boiling 

4212 

water  - 

-  80 

+200 

4392 

-160 

4300 

4572 

4240 

4400 

4752 

4320 

4500 

4932 

4400 

326 


VALUES    OF    FRENCH   AND    ENGLISH 


1°  C.  =  1°.8  Ft.  =  |°  Ft.  =  0°.S  R.  =  f°  R. 
Xf  =  l°Ft.   l°Ft.  x  $  =  1°'C.   1°R.  X!=lc 
X  4  =  1°  R.    1°  Ft.  X  %  =-  1°  R-   1°  R-  X  |  =lc 


Ft. 


Calorie  (French)  =  unit  of  heat  •) 

V  English. 
=  kilogramme  degree  j 

It  is  the  quantity  of  heat  necessary  to  raise  1°  C.  the  tempera- 
ture of  1  kilogramme  of  distilled  water. 

Kilogrammetre  =  Kgm  =  the  power  necessary  to  raise  1  kilo- 
gramme, 1  metre  high,  in  one  second.  It  is  equal  to  ^  of  a 
French  horse  power.  An  English  horse  power  =  550  foot  pounds} 
while  a  French  horse  power  =  542.7  foot  pounds. 

Ready-made  Calculations. 


No. 
of 

units. 

Inches  to 
centimetres. 

Feet  to 
metres. 

Yards  to 
metres. 

Miles  to 
Kilometres. 

Millimetres 
to  inches. 

1 

2.53995 

0.3047945 

0.91438348 

1.6093 

0.03937079 

2 

5.0799 

0.6095890 

1.82876696 

3.2186 

0.07874158 

3 

7.6199 

0.9143835    2.74315044 

4.8279 

0.11811237 

4 

10.1598 

1.2197680    3.65753392 

6.4373 

0.15748316 

5 

12.6998 

1.5239724  14.57191740 

8.0466 

0.19685395 

6 

15.2397 

1.8287669    5.48630088 

9.6559 

0.23622474 

7 

17.7797 

2.1335614 

6.40068436 

11.2652 

0.27559553 

8 

20.3196 

2.4383559 

7.31506784 

12.8745 

0.31496632 

9 

22.8596 

2.7431504 

8.22945132 

14.4838 

0.35433711 

10 

25.3995 

3.0479450    9.14383480 

16.0930      0.39370790 

Xo. 

tin  its. 

Centimetres 
to  inches. 

Metres  to 
feet. 

Metres  to 
yards. 

Kilometres 
to  miles. 

Square  inched 
to  square 
centimetres. 

1 

0.3937079 

3.2808992 

1.093633 

0.6213824 

6.45136 

2 

0.7874158 

6.5617984 

2.187266 

1.2427648 

12.90272 

3 

1.1811237 

9.8426976 

3.280899 

1.8641472 

19.35408 

4 

1.5748316 

13  1235968 

4.374532 

2.4855296 

25.80544 

5 

1.9685395 

16.4044960 

5.468165 

3.1089120 

32.25680 

6 

2.3622474 

19.6853952 

6.561798 

3.7282944 

38.70816 

7 

2.7559553  |22.9662944 

7.655431 

4.3496768 

45.15952  • 

8 

3.1496632  [26.2471936 

8.749064 

4.9710592 

51.61088 

9 

3.5433711   29.5280928 

9.842697 

5.5924416 

58.06224 

10 

3.9370790  32.8089^20 

10.936330 

6.2138240 

64.51360 

10 


WEIGHTS   AND   MEASURES,   ETC. 


327 


No. 
of 

units. 

Square  feet  to 
sq.  metres. 

Sq.  yards  to 
sq.  metres. 

Acres  to 
hectares. 

Square 
•ceati  metres 
to  sq.  inches. 

Sq.  metres 
to  sq.  feet. 

1 

0.0929 

0.836097 

0.404671 

0.155 

10.7643 

2 

0.1858 

1.672194 

0.809342 

0.310 

21.5286 

3 

0.2787 

2.508291 

1.204013 

0.465 

32.2929 

4 

0.3716 

3.344388 

1.618684 

0.620 

43.0572 

5 

0.4645 

4.180485 

2.023355 

0.775 

53.8215 

6 

0.5574 

5.016582 

2.428026 

0.930 

64.5858 

7 

0.6503 

5.852679 

2.832697 

1.085 

75.3501 

S 

0.7432 

6.688776 

3.237368 

1.240 

86.1144 

9 

0.8361 

7.524873 

3.642039 

1.395 

96.8787 

1.0 

0.9290 

8.360970 

4.046710 

1.550 

107.6430 

No. 
of 
onrts. 

Square  metres 
to  sq.  yards. 

Hectares 
.to  acres. 

Cubic  inches 
to  cubic 
centimetres. 

Cubic  feet  to 
cubic  metres. 

Cubic  yards 
to  cubic 
metres. 

1 

1.196033 

2.471143 

16.3855 

0.02831 

0.76451 

•2 

2.392066 

4.942286 

32.7710 

0.05662 

1.52902 

3 

3.588099 

7.413429 

49.1565 

0.08494 

2.29354 

4 

4.784132 

9.884572 

65.5420 

0.11325 

3.05805 

5 

5.980165 

12.355715 

81.9275 

0.14157 

3.82257 

6 

7.176198 

14.826858 

98.3130 

0.16988 

4.58708 

7 

8.372231 

17.29S001 

114.6985 

0.19819 

5.35159 

8 

9.568264 

19.769144 

131.0840 

0.22651 

6.11611 

•9 

10.764297 

22.240287 

147.4695 

0.25482 

6.88062 

10 

11.960330 

24.711430 

163.8550 

0.28315 

7.64513 

No. 
of 
tin  its. 

Cubic 
centimetres  to 
cubic  inches. 

Litres  to 
cubic  inches. 

Hectolitres  to 
cubic  feet. 

Cubic  metres 
to  cubic  feet. 

Cubic  metre* 
to  cubic 
yards. 

1 

0.06102 

61.02705 

3.5317 

35.31659 

1.30802 

2 

0,12205 

122,05410 

7.0634 

70.63318 

2.61604 

3 

0.18308 

183.08115 

10.5951 

105.94977 

3.92406 

4 

0.24411 

244.10820 

14.1268 

141.26636 

5.23208 

5 

0.30514 

305.13525 

17.6585 

176.58295 

6.54010 

-6 

0.36617 

366.16230 

•21.1902 

211.89954 

7.84812 

7 

0.42720    , 

427.18935 

24.7219 

247.21613 

9.15614 

•8 

0.48823 

488.21640 

28.2536 

282.53272 

10.46416 

-9 

0.54926 

549.24345 

31.7853 

317.84931 

11.77218 

10 

0.61027 

610.27050 

35.3166 

353.16590 

13.08020 

It" 


328        FKENCH  AND  ENGLISH  WEIGHTS,   ETC. 


1VT0. 
of 
units. 

Grains 
to  grammes. 

Ounces  avoir, 
to  grammes. 

Ounces  troy 
to  grammes. 

Pounds  aToir. 
to 
kilogrammes. 

Pounds  troy 
to 
kilogrammes- 

1 

2 
3 
4 
5 
6 
T 
8 
9 
10 

0.064773 
0.129546 
0.1  9431  a 
0.259092 
0.323865 
0.388638- 
0.453411 
6.518184 
0.58295T 
0.647730 

28.3375 
56.6750 
85.0125. 
113.3500 
141.6871 
170.0250 
198.3625 
226.7000 
255.0375 
283.3750 

31.0913 
62.1826- 
93.2739- 
124.3652 
155.4565 
186.5478 
217.6391 
248.7304 
279.821T 
310.9130 

0.4534148 
0.9068296 
1.3602444 
1.8136592 
2.2670740 
2.720488S 
3.1739036 
3.6273184 
4.0807332 
4.5341480 

0.373096 
0.746192 
1.119288 
1.492384 
1.865480 
2.238576 
2.611672 
2.984768- 
3.357864 
3.730960 

Pounds  per 

No. 

Long  tons  to>  square  inch  to 

Grammes  to 

Grammes  to 

Grammes  to- 

of 

tonnes  of  1000  kilogrammes 

grains. 

ounces  avoir. 

ounces  troy. 

muits. 

kilog. 

per  square 

centimetre. 

1 

1.015649* 

0.0702774 

15.438395 

0.0352889 

0.0321633- 

2 

2.031298- 

0.1405548 

30.876790 

0.0705778 

0.0643266 

3 

3,046947 

0.2108322 

46.315185 

0.1058667 

0.0964899 

4 

4.062596 

0.2811096 

61.753580 

€.1411556 

0.1286532 

5 

5.078245 

0.3513870 

77.191975 

0.1764445 

0.1608165 

6 

6.093894 

0.4216644 

92.630370 

0.2117334 

0.1929798 

7 

7.109543 

0.4919418- 

108.068765 

0.2470223 

0.2251431 

8 

8.125192 

0.5622192 

123.507160 

0.2823112 

0.2573064 

» 

9.140841 

0.6324966 

138.945555 

0.3176001 

0.289469T 

10 

10.156490 

0.7027740 

154.383950 

0.3528890 

0.3216330 

Metric-  tonnes 

Kilog.  per 

Kilog.  per 

Ho. 

Kilogrammes 

Kilogrammes 

of  1000  kilog. 

square  milli- 

square centi- 

of 

to  pounds 

to  pounds- 

to  long  tons  of 

metre  to 

metre  to 

mnits. 

avoirdupois. 

troy. 

2240  pounds. 

pounds  per 

pounds  per 

square  inch. 

square  inch. 

1 

2.205486 

2.6803 

0.9845919 

1422.52 

14.22526 

2 

4.4109T2 

5.3606 

1.9691838 

2845.05 

28.45052 

3 

6.616458 

8.04091 

2.9537757 

4267.57 

42.67578 

4 

8.821944 

10.7212 

3.9383676 

5690.10 

56.90104 

5 

11.027430 

13.4015 

4.9229595 

7112.63 

71.12630 

6 

13.232916 

16.0818 

P.9U75514 

8535.15 

85.35156 

7 

15.438402 

18.7621 

6.8921433 

9957.68- 

99.57682 

8 

17.643888 

21.4424 

7.8767352 

11380.20 

H  3.  80208- 

9 

19.849374 

24.1227 

8.8613271 

12802.73 

128.02734 

10 

22.054860 

26.8030 

9.8459190 

14225.26 

142.25260 

12? 


HYDROMETERS    AND    THERMOMETERS.  329 


HYDROMETERS  AND  THERMOMETERS. 

An  areometer  is  a  convenient  glass  instrument  for  measuring  the 
density  or  specific  gravity  of  fluids.  Areometer  and  hydrometer 
are  synonymous  terms,  the  first  being  derived  from  the  Greek 
words  apot'oj,  rare,  and  /tftpov,  measure;  and  the  latter  from  -£>5wp, 
water,  and  /teapoy,  measure ;  hence  the  same  instrument  is  fre- 
quently denominated  both  hydrometer  and  areometer.  This  appa- 
ratus is  often  referred  to  throughout  this  work ;  for  instance,  in 
speaking  of  alcohol,  or  lye,  their  strength  is  stated  as  being  of  so 
many  degrees  (17°  or  36°)  Baume,  that  is,  its  force  or  value  is  of 
that  specific  gravity,  corresponding  with  the  degree  to  which  the 
hydrometer  sinks  in  either  the  alcohol  or  alkaline  solution.  But, 
for  those  liquids  lighter  or  rarer  than  water,  viz.,  alcohol,  ethers, 
etc.,  the  scale  is  graduated  differently  than  for  the  heavier  or 
more  dense,  examples  of  which  are  the  acids,  saline  solutions, 
syrups,  and  the  like.  There  are  several  kinds  of  hydrometers; 
but  that  called  Baume*'s  is  the  most  used,  and  to  this  our  remarks 
are  applied. 

They  are  blown  out  of  a  piece  of  slender  glass  tubing,  and  of  the 
form  shown  by  Figs.  124  and  125  ;  A  being  the  stem  containing  the 

Fig.  124.  Fig.  125. 


graduated  paper  scale,  B  the  bulb  portion,  and  D  the  small  globes 
containing  mercury  or  shot,  serving  as  ballast  to  maintain  the 
instrument  in  an  upright  position,  when  it  is  placed  in  a  liquid. 

The  graduation  is  accomplished  by  plunging  it  into  distilled 

water  of  58°  F.,  and  weighting  the  globe  with  shot  or  mercury, 

until  the  instrument  sinks  to  the  line  a,  which  is  its  zero  point. 

This  zero  point  thus  determined  is  to  be  marked  accurately  upon 

50  13 


330  HYDROMETERS    AND   THERMOMETERS. 

the  glass  or  its  accompanying  paper  scale,  and  the  instrument 
.again  plunged  into  ninety  parts  of  distilled  water,  holding  in  solu- 
tion ten  parts  of  previously  dried  chloride  of  sodium  or  common 
salt.  The  point  to  which  it  sinks  in  this  liquid,  say  &,  for  instance, 
is  then  also  marked  carefully  upon  the  scale,  and  rated  as  ten 
compared  with  its  zero  point.  The  interval  between  these  two 
points  is  then  spaced  off  into  ten  equal  divisions,  according  to 
which  the  remainder  of  the  tube  is  graduated  so  that  each  degree 
is  intended  to  represent  a  density  corresponding  to  one  per  cent,  of 
the  salt. 

The  above  mode  of  graduating  refers  to  the  hydrometer  for 
liquids  denser  than  water,  but  that  for  the  liquids  rarer  than  water 
is  a  little  different  from  the  preceding  in  form,  and  necessarily  has 
a  modified  scale,  which  is  graduated  as  is  shown  by  Fig.  125.  The 
instrument  should  be  sufficiently  heavy  in  ballast  to  sink  in  a 
saline  solution  of  ten  parts  of  dried  chloride  of  sodium,  in  ninety 
parts  distilled  water  to  the  bottom  of  its  stem  a,  to  be  marked  as 
the  zero  of  the  scale. 

Now,  when  it  is  again  placed  in  distilled  water  alone,  it  floats  or 
sinks  to  a  point  somewhere  about  6,  which  is  to  be  the  ten  degree 
mark.  The  rest  of  the  stem  is  then  to  be  accurately  divided  into 
as  many  ten  degree  intervals  as  its  length  will  permit,  and  each 
subdivision  into  ten  uniform  smaller  degrees  or  intervals. 
Fig.  126.  As  it  would  be  troublesome,  and  with  many  impracti- 
cable, to  estimate  the  specific  gravities  of  their  liquids 
in  a  scientific  way,  these  little  instruments  are  a  great 
convenience,  for  by  taking  out  a  portion  of  the  fluid  to 
be  tested,  and  placing  it  in  a  glass  cylinder,  Fig. 126, its 
degree  Baume  may  be  ascertained  by  noting  the  point- 
to  which  a  hydrometer  sinks  therein,  and  afterwards 
its  specific  gravity,  by  comparing  that  with  its  corre- 
sponding degree  in  the  table.  For  instance,  suppose 
the  hydrometer  sinks  in  alcohol  to  35°,  then  its  specific 
gravity  is  0.8538,  and  this  again  can  be  translated  into 
its  absolute  spirit  strength  by  comparison  with  any 
accurately  calculated  alcohol  tables.  So,  also,  if  a 
hydrometer  for  liquids  denser  than  water  sinks  in  lye 
to  26°,  it  denotes  that  the  lye  has  a  specific  gravity  of 

14 


HYDROMETERS    AND    THERMOMETERS. 

1  .22(38.  The  presence  of  foreign  matters  will  cause  the  hydro- 
meter to  give  a  false  indication,  and  it  is,  therefore,  necessary, 
when  lyes  contain  impurities,  to  follow  special  directions,  to  as- 
certain their  amount  of  caustic  alkali.  When  the  lye  is  nearly 
pure,  they  answer  satisfactorily;  and,  indeed,  under  all  circum- 
stances, they  serve  very  well  for  noting  a  progressive  increase  or 
diminution  in  the  strength  of  lyes  or  other  liquids.  The  temperature 
of  the  liquid  should  be  583  to  60°  F.,  at  the  moment  of  testing  it. 
Thermometers.  —  The  thermometer  is  an  instrument  made  of 
glass  exclusively,  when  intended  for  practical  purposes.  Fig.  127 
shows  one  with  the  scale  of  Fahrenheit,  graduated  on 


Fig  127. 
the  glass,  so  that,  when  having  been  dipped  in  liquids, 

it  may  be  easily  cleansed.     It  derives  its  name  from 

two  Greek  words,  0*pjtoj,  warm,  and  /*frpoi/,  measure, 

and  is,  as  its  title  indicates,  a  measurer  of  the  variation 

of  temperature  in  bodies.     The  principle  upon  which 

it  is  constructed,  "is  the  change  of  volume  which  takes 

place  in  bodies,  when  their  temperature  undergoes  an 

alteration,  or,  in  other  words,  upon  their  expansion." 

As  it  is  necessary,  in  the  construction  of  thermometers, 

that  the  material  used  to  measure  the  change  of  tem- 

perature shall  be  of  uniform  expansion,  and  with  a 

very  distant  interval  between  its  freezing  and  boiling 

point,  as  fulfilling  these  requisites  better  than  any 

other  body,  metallic  mercury  is  generally  used.    There 

are  several  different   thermometrical  scales,  all   con- 

structed upon  the  same  principle,  but  varying  in  their 

graduation;  the  boiling  and  freezing  points  of  each, 

though   corresponding  in  fact,  being  represented  by 

different  numbers.     The  Fahrenheit  scale  is  most  used 

in  this  country  ;  that  of  Celsius,  called  the  Centigrade, 

in  France  and  the  Continent  generally,  except  Spain 

and   Germany,  where  Reaumur's   scale   is  preferred. 

The  relation  between  the  three  scales  is  shown  03^  Fig.  128.     The 

Fahrenheit  scale  is  most  convenient,  because  of  the  lesser  value 

of  its  divisions. 

In  the  graduation  of  the  scale,  it  is  only  necessary  to  have  two 
fixed  determinate  temperatures,  and  for  these  the  boiling  and 
freezing  points  of  water  are  universally  chosen.  The  scales  can 
be  extended  beyond  either  of  these  points,  by  continuing  the 

15 


332 


HYDROMETERS    AND    THERMOMETERS. 


graduation.  Those  degrees  below  zero  or  0°  have  the  minus  ( — ) 
prefixed,  to  distinguish  them  from  those  above;  thus,  55°  F.  means 
lifty-five  degrees  above  zero,  Fahrenheit's  scale,  and  — 9°  C.,  nine 


degrees  below  zero,  Centigrade  scale.  The  thermometers  for 
general  use  very  seldom,  however,  extend  either  way  beyond  the 
boiling  and  freezing  points  of  water,  but  for  manufacturers'  use 
they  are  graduated  sometimes  to  400°  or  600°. 

Centigrade  and  Fahrenheit. — In  the  Fahrenheit  thermometer 
the  number  0°  on  the  scale  corresponds  to  the  temperature  of  a 
mixture  of  salt  and  ice — the  greatest  degree  of  cold  that  could  be 
artificially  produced  when  the  thermometer  was  originally  intro- 
duced ;  32°  (freezing  point)  corresponds  to  the  temperature  of 
melting  ice;  and  212°  to  the  temperature  of  pure  boiling  water — 
in  both  cases,  under  the  ordinary  atmospheric  pressure  of  14.7 
pounds  per  square  inch.  Each  division  of  the  (this)  thermometer 
represents  1°  Fah.,  and  between  32°  and  212°  there  are  180°.  In 
the  Cent,  thermometer,  used  universally  in  scientific  investigations, 
1°  corresponds  to  molting  ice,  and  100°  to  boiling  water.  From 
the  freezing  to  the  boiling  point  there  are  100°. 

The  accompanying  table  shows  the  relation  of  the  Centigrade 
and  Fahrenheit  thermometer  scales,  5°  C.  being  equal  to  9°  F., 
because  the  interval  between  the  freezing  and  boiling  points  of 
water  is  divided  into  100  and  180  equal  parts,  and  these  numbers 

16 


HYDROMETERS   AND   THERMOMETERS.  333 

are  respectively  multiples  of,  or  20  times  5  and  9.  If  the  super- 
fluous 32°  on  the  F.  side  were  disposed  of,  the  mutual  translation 
of  the  scales  would  be  simple,  since  the  two  units  are  to  each 
other  inversely  as  the  number  of  them  in  any  given  range. 

To  reduce  F.  above  melting  ice  to  terms  of  C.,  32°  must  first  be 
subtracted  from  the  given  F.  temperature,  then  multiply  the  re- 
mainder by  -§• ;  the  product  will  be  the  C.  term  for  the  given  tem- 
perature; and  conversely  divide  C.  by  f  and  add  32  to  translate 
C.  into  F.;  to  prove  the  work,  read  the  terms  across  the  diagram 
in  the  table.  *  Below  melting  ice,  the  same  rules  as  given  above 
apply,  except  that  where  32  is  added  above,  it  should  be  subtracted 
here,  and  vice  versa. 

In  the  columns  at  the  right  hand  of  each  diagram  in  this  table, 
are  found  the  approximate  steam  pressures  per  square  inch,  due 
to  the  adjoining  indications  of  temperature.  The  pressure  is 
expressed  in  pounds  and  in  atmospheres. 

The  high  pressures  are  obtained  from  the  several  authors  who 
have  deduced  and  tabulated  them  from  experiments  and  formulas 
of  Regnault  and  others ;  and  being  hypothetical,  accuracy  is  not 
claimed  for  them. 


334 


HYDROMETERS    AND    THERMOMETERS. 


COMPARISON  OF  CENTIGRADE  AND  FAHRENHEIT  SCALES,  AND  APPitOS.. 

IMATE   STEAM  PRESSURE  IN  POUNDS  AND  ATMOSPHERES 

PER   SQUARE   INCH  DUE  TO  THE   TEMPERATURE. 


THERMOMETER. 
Conti.      Fa'ur. 


260 
255 
250 
245 
240 
235 
230 
225 
220 
215 
210 
205 
200 
195 
190 
185 
180 
175 
170 
165 
160 
155 
150 
145 
140 
135 
130 
125 
120 
115 
110 
105 


500 
491 
482 
473 
464 
455 
446 
437 
428 
[419 
410 
401 
392 
1383 
574 
55 
556 
J47 
538 
529 

111 

103 

593 

584 

|275 

260 

1257 

1243 

539 

1230 

J21 


STEAM. 
NON-CONDENSING  ENGINE. 


Pres.  per 

gauge. 

Ibs. 


665 

610 

560 

515 

'472 

430 

390 

354 

321 

290 

262 

235 

211 

183 

1G7 

143 

131 

115 

100 

85 

73 

GO 

55 

45 

37 

30 

25 

19 

14 

10 

6 

3 


Total  Press. 
Lbs.      Atmos. 


680 

625 

575 

530 

487 

445 

405 

369 

336 

305 

277 

250 

220 

203 

182 

163 

140 

ICO 

115 

100 

83 

73 

70 

60 

52 

45 

40 

34 

29 

25 

21 

13 


46. 

42. 

39. 

36. 

33. 

30. 

27.5 

25. 

23. 

20.7 

18.8 

17. 

15.8 

13.8 

1D.4 

11.1 
9.C 
8.8 
7.C 
6.C 
6. 
5.C 
4.7 
4.1 
3.C 
3. 
2.7 
2.C 
1. 
l.C 
1.4 
1.2 


THERMOMETER. 


Centi. 


100 
95 
90 
85 
80 
75 
70 
05 
GO 
55 
50 
45 
40 
35 
30 
25 
20 
15 
10 

5 

0 

—  5| 
—II 
—151 
— 2( 
—251 
—3 
—35 
—401 
—45 


Fahr. 


1212 
203 

194 

185 
176 
167  | 

L| 

1 140  | 
1315 
122 
113 
1104 

05 

86  J 

77 

68 

59 

50, 

41 

32 

23 

14 

5 

0 
—  4 

—13 
—22 
—31 
—40 

—48 


STEAM. 
CONDENSING  ENGINE. 


Press,  per        Back  Press^ 
gauge.  Lbs.    Atmos. 


Vacuum,  effective. 
Gauge.       Lbs.* 


12$ 


20$ 

22 

24 

25 

26 

26$ 

27f 

28$ 

29 


4.7 

6.2 

7.7 

D.I 

10.2 

11. 

11.9 

12.4 

12.9 

13.3 

13.6 

13.8 

13.9 


14.7  !  1. 


Lbw.          Aliuos 


12. 
10. 

8.5 


0.7 
0.6 
0.5 
04 
0.3 


5.6 

4.5 

3.7 

2.8  i  0.2 

2,3 


1.8 

1.4 

1.1 

.9 

.8 


0.2 


0.1 


*  To  be  added  to  the  pressure 
indicated  by  steam  gauge  to 
get  total  pressure  on  piston. 


M.  T.  Mines  of  Brittany, 

5G011 59  F. 

Hydrochloric  Ether  boils,  C2  F. 

Max.  density  of  water,  -  _7r.' 

Melting  Ice,  .  32  F.  =0  C. 
Blood  freezes,  .  .  25  F. 
Castor  Oil  freezes,  .  21  F. 
Spirits  of  turpentine 

freezes,        .        .       14  F. 


Brandy  freezes, 


— 7F. 


Mercury  freezes,       .    —40  F. 
Sulphuric  Acid  (1.641) 

freezes,         .       .    —  43  F. 

Greatest  artificial 

cold,      .     —  166  to—  220  F. 


Absolute  cold,      .  j  Z^g'4  £' 


18 


INDEX. 


A  BSTRICH,  90 

X\_     Acid  copper  solutions  in  electro- 
lytic assays  of  nickel,  196 
solvent  agents,  77 
Acids  for  wet  assays,  80 
Air  baths,  24 

excluding  fluxes,  79 

ignition  with  admission  of,  31 

exclusion  of,  31 
Alibegoff  on  assay  of  uranium,    256, 

257 

Allen  on  examination  of  New  Cale- 
donia nickel  ores,  198,  199 
Alloys,  gold,  free  from  copper,  pre- 
liminary test  for,  168,  169 
of  copper,  assay,  104 
of  gold  and  silver,  with  or  with- 
out copper,  168-181 
assaying,  167-184 
with   copper,    separated    by 

cupellation,  181 
with  silver  and  copper,  quan- 
tity of  lead  required,  169, 
170 

of  lead,  wet  assay,  92-95 
of  platinum,  186,  187 

electrolytic  assay  of,  187 
sampling  of,  22,  23 
weighing,  29 

Almaden,  mercury  assays  at,  242 
Amalgam,  silver,  dry  assay  of,  143 
American  assay  weights,  70 
Ammoniacal  nickel  solutions,  in  elec- 
trolytic assays  of  nickel,   196 
Ammonium  carbonate,  79 
Anglesite,  81,  91 
Antimonial  nickel,   187 

ore,  188 
silver,  128 

Antimonium  crudum,   liquation    pro- 
cess for  determining,  243 
Antimony,  243-250 

assay  of,   by  precipitation,   243, 

244 
of  lead  ore  containing,  88 


assaying, 


Antimony — 

Becker's    method    of 

245,  246 
detection  of  tin  in  presence  of, 

232 
determination    of,    in   antimony 

sulphide,  243 
electrolytic  determination  of,  249, 

250 

fire  assays  of,  243,  244 
gravimetric  assay,  245,  246 
in  copper,  removal  of,  105 
in  nickel  compounds,  removal  of, 
-  194 
ores,  243 
oxide,  243 

as  a  flux,  79 
oxysulphide.  243 
prevents  copper  from  slagging,  99 
roasting  and   reducing  assay   of, 

244 
sulphide,  243 

inaccuracy  of  the  assays  of, 

243 
volumetric  estimation  of,  in  the 

presence  of  tin,  249 
Weil's    method  of  determining, 

246-249 

wet  assays,  245-250 
Apothecary  balance,  69 
Argentiferous  gold,   boiling,  in  nitric 

acid,   174,  175 
roll  assay  for,  172-177 
lead,  cupellation  of,  138-141 
Arsenates  of  copper,  96 
Arsenic,  251-255 

acid,   reduction   of  to  arsenious 

acid,  254 
as  a  flux,  79 
fire  Jtssays  of,  251,  252 
gravimetric  assays  of,  252,  253 
in  copper,  determination  of,  127 
in  copper,  removal  of,  105    • 
in  glass,  255 
native,  251 


336 


INDEX. 


Arsenic —  * 

ores  of,  251 

Pearce's   method   of  determina- 
tion of,  254,  255 
prevents  copper  from  slagging,  99 
volumetric  assays  of,  254,  255 
wet  assay,  252,  253 
wet  assays  of,  252-255 
wet  method  combined  with  the 

dry,  253 
Arsenical  iron  in  nickel  ores,  slagging 

off',  191 
Arsenious  acid,  251 

estimation  of,  254 
Arsenizing  nickel  ores,  188,  190 
Assay  furnaces,  45-63 

for  charcoal,  illustrated  and 

described,  49 
liquid,  measuring  and  titration  of 

the,  42-44 
of  lead  with  potassium  cyanide 

in  clay  crucibles,  84,  85 
of  platiniferSus  ores,  185,  186 
reagents,  74-80 
vessels,  63-69 

for  the  dry  method,  63-68 
for  the  wet  method,  68,  69 
Assaying,  object  of  the  art  of,  17,  18 
various   methods  employed,   17, 

18 

Assays  of  lead  in  the  dry  way,  81-92 
Atacamite,  96 
Atomic  weights,  297 
AugendreVs  process  of  cupelling  gold, 

179,  180 

Auriferous  bismuth,  167 
iron,  168 
lead,  167 

cupellation  of,  166,  167 
pyrites  in  gold  tailings,  165 
silver,    gold   determined    in,    by 

Volhard's  assay,  181 
grains,    separation   of,  from 

samples  of  ores,  181 
pulverulent  assay   of,    180- 

184 

steel,  168 

Austrian  assay  weights,  69 
Azurite,  96 


T)ALANCE,    manipulation  of  the, 
D     28,  29 

Balances  and  weights,  69,  70 
Balling's    method    of   quartation    of 
gold  with  cadmium,  181,  182 


Barium  chloride,  80 
Bases  and  salts  for  wet  assays,  80 
Basic  solvent  agents,  77,  78 
Becker's    method   of    assaying   anti- 
mony, 245,  246 
improved    by   Do- 

nath,  245 

Beilstein  and  Jawein  on  the  determin- 
ation of  cadmium,  223 
electrolytic    assay    of    zinc, 

210,  211 

Belani's  method  for  manganese,  275 
Belgium,  assay  of  lead  matt  in,  84 
Berlin  School  of  Mines,  furnaces  used 
in  the,  illustrated  and  described,  53- 
55 

Berthier  on  the  reducing  power  of  va- 
rious agents,  75,  76 
method  for  the  dry  assay  of  iron 

ores,  310 

of  determining  absolute  heat- 
ing power  of  fuel,  288- 
290 

Berzelius's  method  of  assaying  tung- 
sten, 259 

Bischof,  assay  of  lead  by,  94 
Bismuth,  233-236 
auriferous,  167 
determination   of  percentage   of 

lead  and  silver  in,  236 
electrolytic  precipitation   of,    by 

Smith  and  Knerr,  236 
fire  assays  of,  234,  235 
glace,  233 

in  copper,  removal  of,  105 
in  silver  alloy,  treatment  of,    151 
native,  234 
ochre,  233 
ores,  233 

and   compounds    free    from 

sulphur,  234 
Joachimsthal     process     for, 

234,  235 

Rose's  process  for,  235 
sulphurized,  234,  235 
Tamm's  process  for,  234,  235 
Ullgreen's  process  for,  236 
oxide,  205 
separation   of,    from   lead,    235, 

236 

wet  assays  of,  235,  236 
Bismuthic  cupel  ash,  234 
Bitumen  in  copper,  removal  of,  105 
Black  flux,  74,  75,  77 

and  metallic  iron,  assay  of 
galena  with,  85-87 


INDEX. 


337 


Blast  furnaces,  59-61 

lamp,    best   form    of,    illustrated 

and  described,  39,  40 
Bleiberg,    Carinthia,     assay    of    lead 

matt  in,  84 
gravimetric  assays  of  lead  in, 

92,  93 
Blowpipe,   refining  copper   ore  with 

the,  103 

use  of,   in  assaying,  18 
Blue  vitriol,  96 
Bockmann's   method  of  determining 

sulphur  in  py rite's  waste,  281 
Bock's  experiments  on   gold   alloys, 

179 
Bodewig's    method    for  determining 

sulphur,  280,  281 
Boiling  argentiferous    gold   in   nitric 

acid,  1  74,  1  75 

Bone  ash,  making  cupels  of,  66 
Borax  glass,  77 

refining  copper  on  the  dish  with, 

99,  100 
use  of,   in  scorification   assay  of 

silver,  130 
Bournonite,  95,  96 
Braunite,  264 
Breithauptite,  187 
Bromyrite,  128 
Bronze,  assay  of,  119 
Brown,  Walter  L.,  charge  for  gold 

ores  containing  tellurides,  1 C6 
Brunnlechner's  modification  of  Schaflf 

ner's  assay  of  zinc,  303-307 
Brussels,  mint  of,  assaying  gold  coins 

at,  179,  180 

Bullion  or  button  balance,  69 
Bullion,  silver,  assays  of,  155 
Bunsen's  method  for  manganese,  270- 

272 
Bunte's  burette  for  the  examination 

of  furnace  gases,  294,  295 
Burettes,  illustrated,  43,  44 
Button,  weighing  the,  29 


nADMIUM,  222,  223 

\J    and  zinc,  separation  of,  222 

determined  in  the  same  way  as 

zinc,  223 

electrolytic  assay  of,  222,  223 
in  an  ammoniacal  solution,  pre- 
cipitation of,  222 
in  neutral  acid  solutions,  precipi- 
tation of,  222 
22 


Cadmium — 

in  solutions  of  ammonium  or  po- 
tassium   double   oxalate,    pre- 
cipitation of,  223 
ores,  222 

quartation  of  gold  with,  181,  182 
sulphide,    precipitation    of,  from 

an  acid  solution,  222 
Calamine,  207 
Calcining  vessels,  64 
Calcium  carbonate,  77 

fluoride,  77,  78 

Canby's    simplification    of    Pearce's 
method  of  determining  arsenic,  255 
Carbon,  desulphuration  with,  78 

in  fuels,  yield  of,  285,  286 
Cassiterite,  223 
Caustic  alkalies,  77 

and  carbonates,  78 
carbonates,  78 
Centner,  assay,  69 
Cerusite,  81,  90,  91* 
Chamotte,  63 
Charcoal  and  coke  furnaces,  49 

and  graphite,  79 
Charging  the  sample,  30,  31 
Chemical  operations,  31-45 

classification  of  the,  31 
Chlorination  process,  Plattner's,  167 
Chrome  iron  ore,  261 

Calvert's,        Britton's, 
Dittmar's,     Hager's, 
Fels's,    and   Clarke's 
methods  for    decom- 
posing, 263 
Chromium,  261-264 
direct  assay  of,  262 
gravimetric  assays  of,  262,  263 
indirect  assay  of,  263 
ores  of.  261 

volumetric  assay  of,  263,  264 
wet  assays  of,  261-264 
Cinnabar,  236 
assay  of,  241 

treatment  with  aqua  regia,  241 
Clamond's    thermo-electric    battery, 

111 

Clark  on  assay  of  cadmium,  222 
Classen  on  electrolysis  of  tin,  233 

on  electrolytic  assay  of  silver,  160 
of  platinum,  187 
of  zinc,  213 
determination    of    mercury, 

242 
on  precipitation  of  cadmium,  223 


338 


INDEX. 


Classen's  method  for  the  electrolytic 

determination  of  metals,  114-116 
Clay  vessels,  63-65 
Coal,  determination  of  coking  quality 

of,  286 

of  copper  in  ash  of,  286,  287 
of  sulphur  in,  287 
of  volatile  products  of,  286 
Cobalt,  204-207 

and  nickel,   difficult  to  separate 

from  copper,  99 
in  nickel  ores.  Donath's  as- 
say of,  203,  204 
separation  of  in  nickel  ores, 

201 

tints  produced  by,  156 
arsenide  in  nickel  ores,  slagging 

off,  191 

arsenide,  slagging  off,  191 
assays  of,  204-207 
beauty  of  the  colors  of,  204 
bloom,  204  • 
color,    assay    to    determine    the 

quality  of,  206 
intensity  of,  206,  207 
quality  of,  206 
determination  of,  204 

of  the  bl.ue  coloring  power 

in,  204 

dry  assay,  204 
glace,  204 

in  nickel  ores,  separation  of,  203 
in  speiss,  electrolytic  determina- 
tion of,  199,  200 
metallic  oxides  in,  205 
object  of  the  smalt  assay  of,  205 
ores,  204 

containing  copper  and  nickel, 

roasting  of,  205 
entirely   pure,    roasting    of, 

205 

impure,  roasting,  205 
roasting  of,  205,  206 
pyrites,  204 
smalt  assay,  204-206 
wet  assay,  204 
Cobaltine,  204 
Cobaltous  oxide,  204,  205 
Cobenzl's  method  of  assaying  tun<r- 

sten,  260 

Coins,  mint  assay  of,  144 
nickel,  assay  of,  117 

determining   the  copper  in, 

201,  202 

samples  for  producing,  23 
sampling,  22 


Coke  and  charcoal  furnaces,  49 

anthracite,  and  graphite,  substi- 
tutes for  charcoal,  74 
Coke  cupels,  68 
Colorimetric  analysis,  17 
assays  by,  44,  45 
vessels  for,  68,  69 
assays,  when  employed,  18 

of  copper,  104,  125-128 
Combustion   furnace,   illustrated   and 

described,  238 

Comparison  of  Centigrade  and  Fah- 
renheit   scales     and     approximate 
stearn  pressure  in  pounds  per  square 
inch  due  to  the  temperature,  334 
Concentrating  iluxes,  78,  79 
Copper,  95-128 

alloyed  with  tin,  assay  of,  119 
alloys  of,  assay,  104 
and  silver  in  one  solution,  deter- 
mination of  silver  in,  157 
arsenates  of,  96 
as  recently  precipitated  sulphide, 

treatment  of,  116 
assay,  Cornish,  96,  104 
of,  by  Haen,  125 
of,  with  protochloride  of  tin, 

124,  125 

of,  with  sodium  sulphide  in 
an  ammoniacal  solution, 
124 

of,  with  sulpho-cyanide,  118 
Classen's  electrolytic  determina- 
tion of,  115,  116 
colorimetric  assays  of,  104,  125- 

128 
determination  of  arsenic  in,  127 

of  phosphorus  in,  127 
difficult   to   separate   nickel  and 

cobalt  from,  99 
dry  assays  of,  96-104 
electrolytic  assays  of,  110-116 
Fleitman's   assay  of',  with  ferric 

chloride,  122,  123 
glance,  95 
gravimetric  assays,  104-119 

method  for  the  determina- 
tion of  (Genth's),  109, 
110 

Heine's  assay  for,  125,  12t> 
Herpin's  method  of  testing,  113 
Jaquelin  Hubert's  assay,  for  con- 
siderable percentages  of,   126, 
127 

impure  (black)  precipitated,  ex- 
amination of,  105 


INDEX. 


339 


Copper — 

indications  of  a  successful  assay 

98 

in   nickel  coins,  solution  for  de- 
termining, 201,  202 
in  speiss,  electrolytic  determina- 
tion of,  199.  200 
in  the  form  of  cuprous  sulphide, 

determination  of,  116,  117 
lead,   and   zinc  in   one  solution, 

determination  of,  221 
Lower  Harz   working  assay   of, 

302 

nickel,  187 

ore,  American  charge,  98,  99 
assay  with  lead   and   borax 
(Musen  assay),   101,   10: 
containing    much    iron,    co 
bait,  or  nickel,  treatment 
of,  101 

MUsen  assay  of,  101,  102 
not    containing    lead,    anti- 
mony, nor  zinc,  assay  of, 
101 
refining,  99 

by  cupellation,  102,  103 
with  the  blowpipe,  103 
ores,  95,  96 

charges  of,  98,  99 
containing    bitumen,    treat- 
ment of,  105 
differences  allowed  in  assays 

of,  101 
oxidized,    without    sulphur, 

treatment  of,  103,  104 
reducing  and  solvent  fusion, 

97. 
roasting,  97 

very  poor,  fusing  of,  in  larger 

quantities,  103 
with  antimony  or  zinc,  95 
with  sulphur,  antimony,  or 
arsenic,  treatment  of,  97- 
103 

oxide  as  a  flux,  79 
Parkes's   assay,    with   potassium 

cyanide,  120-122 
phosphates  of,  96 
poor  in  silver,  dry  assay  of,  143, 

144 
precipitated,  correction  for  iron 

in,  107 

with  iron  or  zinc,  105 
precipitation  of,  by  the  galvanic 

current,  110,  192,  193 
with  iron,  106-108 


Copper,  precipitation — 

with  zinc  free  from  lead  and 

arsenic,  108,  109 
prevention  of  slagging,  99 
pure  precipitated,  color  of,  107 
pyrites,  95,  276 

treatment  of,  97 

red,   indication  of  arsenic,  anti- 
mony, or  selenium  in,  112 
reducing  with  potassium  cyanide, 

119 

refined,  Hampe's  method  of  test- 
ing, 113,  114 
refining  by  itself,  without  borax 

and  lead,  100,  101 
on  the  dish  with  borax,  99, 

100 

removal  of  tin  and  zinc  from,  99 
slag,  treatment  of,  99 
Steinbeck's  method  of  assaying, 

122 

sulphide,  130 
Swedish  assay  for,  105 
testing  for,  in  the  ore  residue,  107 
various  reducing  processes,  1 1 9 
volumetric  assays  of,   104,   119- 

125 

Weil's  method  for  reducing,  119 
wet  assays  of,  104-128 
Cornish  assay  of  tin,  227 

less   accurate   than   the 

German,  224 
copper  assay,  96,  104 
Cornwall,    determination   of   tin    in, 

223,  224 
Crocoisite,  81,  90,  261 
Cross  method  of  sampling,  19,  20 
Crucible  assay  for  gold  ores,  162,  163 

use  of,  1 29 
Crucibles  for  assay  of  lead,  65,  66 
for  dry  assay  of  iron  ores,  311 
for  lead  and  copper  smelting,  il- 
lustrated, 65 
for  smelting  iron,  65 
illustrated,  64,  65 

upel,  loss  of  silver  by  absorption  of, 
146,  147 
!upels,  coke,  68 

mould  for  making,  66 
of  bone-ash,  66-68 
simple  machine  for  making,  illus- 
trated, 67,  68 
upellation   of    the   auriferous   lead, 

166,  167 

preliminary  assay  of  cupriferous 
alloys  by,  169,  170 


340 


INDEX. 


Cupellation — 

refining  copper  by,  102,  103 
Cupric  oxide,  205 
sulphate,  96 

decomposition  of,  103 
Cupriferous  alloys,  preliminary  assay 

of,  by  cupellation,  169,  170 
bismuth,  233 
compounds  of  nickel  ores,  assays 

of,  191-194 
wet  assay  for,  192 
rich  in  copper,  assay  for,  192 
•with  small  percentage  of  cop- 
per, assay  for,  192 
schists,  treatment  of,  105 
silver,  dry  assay  of,  144-147 
Cuprite,  96 
Cuprous  oxide,  205 

schist,  treatment  of.  109 
sulphate  with  calcium  and  barium 
sulphates,     decomposition     of, 
103,  104 

sulphide,   determination  of  cop- 
per in  the  form  of,  116,  117 


T\EAESENIZING  nickel  ores,  191 
JL/     Debray's  apparatus  for  precipi- 
tation,    illustrated     and     de- 
scribed, 38 
Decantation,  39 
Decomposing  and  volatilizing  fluxes, 

79 

Decrepitated  common  salt,  79 
Desiccated  mass,  pulverizing  the,  25 
Desiccator,  illustrated  and  described, 

40 

Desulphuration  with  carbon,  78 
Desulphurizing  agents,  78 
Determination  of  moisture,  24 
Deutocom's  method  for  determining 

sulphur,  280 
Deville's  furnace,  59 
D'Hennin's    process     of    separating 

iridium  from  gold,  178 
Dioptase,  96 

Dipping,  sampling  by,  23 
Distillation  and  sublimation,  35 

furnace,  illustrated  and  described, 

61-63 

Docimacy,  17 
Donath's  assay  of  nickel  and  cobalt, 

203 
improvement  of  Becker's  method 

of  assaying  antimony,  245 
Draught  or  wind  furnaces,  51-59 


Dropping  the  ore,  sampling  by,  20,  21 
Dross,  lead,  91 

silver,  1-38 

Drown's  method  of  determining  sul- 
phur in  coal,  290,  291 
Dry  assay,  1 7 

assays,  reagents  for,  74-79 

method,  working  by  the,  31-35 
Drying  disk,  illustrated,  24,  25 

precipitates,  39 

Ducktown,  Tennessee,  assaying  cop- 
per at  the  copper  works  of,  122 


T1ARTHY  cobalt,  204 
jQj     Electrolysis,  17 

separation  of  gold  from  plati- 
num by,  183,  184 
assay  of  nickel,  1 94-200 

of    zinc    by    Beilstein    and 

Jawein,  210,  211 
assays  of  manganese,  275,  276 
determination  of  antimony,  249, 

250 
of  copper,  nickel,  and  cobalt 

in  speiss,  199,  200 
of  mercury,  242 
of  metals  (Classen's),   114- 

116 

of  silver,  159,  160 
of  tin,  232,  233 
processes,  assays  of  lead  by,  94, 

95 

Enargite,  96 
England,  assay  of  galena  in,  86,  87 

of  lead  matt  in,  83,  84 
English  assay  weights,  69,  70 

commission  on  errors  in  assay  of 

coins,  1  77 

Erhard  and  Schertel's  determinations 
of  the  fusing  points  of  metals,  alloys, 
etc.,  300,  301 
Erubescite,  95 

Eschka's  assay  of  mercury,  239-241 
Escosura  on  the  electrolytic  determi- 
nation of  mercury,  24  2 
Evaporation  of  the  solution,  37 


T71AHLERZ,  95 

Jj      Ferric  chloride,  80 

,         Fleitman's  assay  of  copper 

with,  122,  123 
hydrate,  retention  of  copper* by, 

126 
oxide,  78,  205 


INDEX. 


341 


Ferrous  ammonium  sulphate  solution, 

preparation  of,  183 
oxide,  205 

prevents  copper  from  slag- 
ging, 99 

Fikentscher-Nolte  method  for  assay- 
ing manganese,  268,  269 
Filtering  apparatus,  illustrated,  38 
Filtration,  38 

Final  reaction,  determining  the,  40,  41 
Fire  assays  for  silver,  129-142 
Flasks,  measuring,  illustrated,  42 
Fleitman's  assay  of  copper  with  ferric 

chloride,  122,'  123 

Fletcher's   direct-draft    crucible   fur- 
nace, illustrated  and  described, 
57.  58 
injection  gas  furnace,  illustrated 

and  described,  60,  61§ 
Flintshire,  assay  of  lead  in,  *84 
Fluor  spar,  77,  78 
Fluxes,  78,  79 

for  the  dry  assay  of  iron  ores, 

313,  314 

measuring  of,  29,  30 
weighing,  29 
Fragments,    homogeneous,    sampling 

of,  19 

heterogeneous,  sampling  of,  19-22 
Franklinite,  207 
Frederickshutte,  assay  of  lead  ore  in, 

84 
Freiberg,  assay  of  galena  at,  86 

results  obtained  at,  regarding  ab- 
sorption by  the  cupel,  147 
French    and    English    weights    and 
measures,    tables    of    relative 
value  of,  321-328 
Commission     on     Coinage     and 
Metals,  correction  table  of,  for 
absorption  by  the  cupel,  147 
Fresenius  on  the  sources  of  error  in 
processes   for  detecting  sulphur  in 
pyrites,  280 
Fresenius's   drying   disk,   illustrated, 

24,  25 
Fresenius-Will   method  for   assaying 

manganese,  267,  268 
Fuel,  amount  of  ash  in  different  kinds 

of,  287 

assays  of,  285-291 
determination  of  absolute  heating 

power,  287 
of  ash  in,  286 

of  heating   power   of,    287, 
288 


Fuel,  determination— 

of  hygroscopic  water  in,  285 
removal    of    earthy    admixtures 

from,  284 

yield  of  carbon  from,  285,  286 
Fuels,  284-291 

composition  of,  284 

physical  and  chemical  behavior 

of,  291 
Furnace,  Brown's  gas,  illustrated  and 

described,  58,  59 
distillation,    illustrated    and   de- 
scribed, 61-63 

Fletcher's  direct-draft  crucible, 
illustrated  and  described, 
57,  58 

injector,  gas,  60,  61 
for    melting   with    a    coke   fire, 

illustrated  and  described,  57 
gases,  examination  of,  291-295 
Perrot's  gas  muffle,  illustrated 

and  described,  50,  51 
illustrated  and  described,  54, 

55 

Roessler's,  for  production  of  high 
temperatures,    illustrated    and 
described,  56,  57 
sublimation,   illustrated  and  de- 
scribed, 61 
taking  the  vessels  from  the,  52, 

53 

tools,  70 

W i ess n egg's  gas,  56 
Furnaces,  assay,  45-63 
blast,  59-61 
charcoal  and  coke,  49 
draught  or  wind,  51-59 
firing,  52 

for  free-burning  coal,  55 
for  illuminating  gas,  55 
for   solid,    free-burning,   flaming 

fuel.  46-49 
for  sublimation  and  distillation, 

61-63 

labor  attending,  52 
muffle,  45-51 

oil,  of  Andouin-Deville,  50 
organic  combustion,  63 
used  in  the  Berlin  school  of  mines, 
illustrated  and  described,  53- 
55 

Fusing  points  of  metals,  alloys,  fur- 
nace products,  rocks,  and 
silicates,  according  to  Er- 
hard  and  Schertel,  300, 
301 


342 


INDEX. 


Fusing  points — 

of  metals  and  furnace  pro- 
ducts,   glowing    tempera- 
tures, 298,  299 
Fusion,  34,  35 
liquating,  35 
mixing,  35 
oxidizing,  34 
precipitating,  35 
purifying,  35 
reducing,  34,  35 


GALENA,  81 

\JC    assay  in  an  iron  pot,  82,  83 
Belgian  assay  of,  82,  83 
containing     large    quantities    of 

earths,  assay  of,  88 
rich,  assay  of,  82-85 
with  more  earths,  assay  of,   85- 

88 

with  zinc  blende,  pyrites,  etc.,  88 
etc.,  without  foreign  metallic  sul- 
phides, 81 

Galetti  on  the  effect  of  manganese- 
zinc,  219 

titrating  solution,  219 
volumetric  assay  of  copper,  119 
Garnierite,- 188 
Gas  furnaces,  50,  51 
Gay   Lussac's    apparatus,    illustrated 

and  described,  150,  151 
assay  of  silver  bullion,  155 
tables   for   determining    the 
fineness   of   silver   alloys, 
152-154 

Genth,   Dr.,  gravimetric  method  for 
the  determination  of  copper,  109, 
110 
Gerlach's  method  for  assaying  sulphur 

earths,  277 
German  assay  of  tin,  224 

more  accurate  than  the 
English  or  Cornish, 
224 

copper  assay,  96-104 
smelting  works,  sampling  in,  21 
Gersdorffite,  188 
Glass,  79 

containing  arsenic,  255 
Glaucodot,  204 
Gold,  1C  1-1 84 

alloys,    Bock's   experiments   on, 

179 

determination  by  color,  168, 
109 


Gold,  alloys — 

effects  produced  by  various 
metals  in  cupelling,  179, 
180 

examination  of,  on  the  touch- 
stone, 169 
free  from  copper,  preliminary 

test  of,  168,  169 
preparation   of    the    ferrous 
ammonium  sulphate  solu- 
tion, 183 

amalgam,  167,  168 
and  silver  alloys,  with  or  without 

copper,  168-181 
sweepings,  crucible  assay  of, 

135-138 
with    platinum,    cupellation 

of,  186,  187 
as  a  flux,  79 

brittle,  toughening  of,  184 
button,  laminating  the,  173,  174 
coins,    standards    of,   in   various 

countries,  171 

etc.,  appreciable  quantity  of 
the  platinum  group,  metals 
found  in,  180 

cupelling  of,  to  obtain  best   re- 
sults, 178,  179 

fire  or  fusion  assays  of,  162-167 
Juptner's    volumetric    assay    of, 

182,  183 

loss  of,  in  cupelling,  176 
Lower  Harz,  working  assay  of, 

303 
mechanical    assay    by    washing, 

161,  162 
native,  161 

non-alloys,  assay  of,  161-167 
ores,  161 

American,  assay  of,  163 
assay  with  nothing  but  lith- 
arge as  a  flux,  163,  164 
containing   tellurides,    assay 

of,  165,  166 

crucible  assay  for,  162,  163 
scorification  assay  for,  162 
wet  assay,  167 
with  earths  and  oxides,  163, 

164 

etc.,  with  sulphur,  anti- 
mony, or  arsenite,  164- 
166 

ore  tailings,  165 
pure,  preparation  of,  171,  172 
pyrites  poor  in,  164,  165 
quartz,  163 


INDEX. 


343 


Gold- 
separation  of,  from  platinum  by 

electrolysis,  183,  184 
of  iridium  from,  by  fusion, 

178 

slag,  163 

smelting  with  lead,  162-166 
superheating  of,  178,  179 
sweepings,  163 
with  cadmium,  quartation  of,  181, 

182 
with    platinum,    cupellation    of, 

180,  186 
Goldsmith's  sweepings,  sampling,  20, 

21 

Gorz,  results  obtained  by,  in  assaying 
sweepings  and  other  refuse  from 
the  manufacture  of  silverware,  137, 
138 

Gramme  weight,  69 
Granulation,  sampling  by,  23 
Graphite  and  charcoal,  79 

crucibles,  65 
Gravimetric  analysis,  1 7 

assay  of  lead  by,  92-94 
assays  by,  35-40 
of  silver  alloys,  158,  159 
vessels  for,  68 
assays  for  copper,  104-119 
Greenockite,  222 


HAEN'S  assay  of  copper,  125 
Hampe's  method  for  manganese, 

274,  275 
of    testing    refined    copper, 

113,  114 
Hart  on  the  volumetric  assay  of  tin, 

231 

Hausmannite,  264 
Heating  power  of  fuels,  determination 

of,  287,  288 

Heat-regulator  at  United  States  Assay 
Office,  New  York,  experiments  on, 
307-309 
Heine's  assay  for  poor  copper  ores, 

etc.,  125;  126 
col ori metric    assay   for   products 

poor  in  copper,  302 
Herpin's  method  of  testing  copper,  113 
Hessite,  128 
Heterogeneous    fragments,    sampling 

of,  19-22 
Homogeneous  fragments,  sampling  of, 

19 
Horn  silver,  128 


Hungarian     mercurial     tetrahedrite, 

237,  238 
smelting  works,  assay  of  gold  at, 

165 

speiss  assays  of  copper,  100-101 
Hungary,  assay  of  lead  in,  88,  89 
Hydrogen,  apparatus  for  igniting  in  a 
.  current  of,  illustrated  and  described, 

117,  118 
Hydrometers  and  thermometers,  329- 

333 

Hydrostatic  assay  of  silver  coins,  160 
Hygroscopic    substances,    convenient 

weighing  of,  29 
water  in  fuels,  285 


IDRIA,  mercury  assay  at,  237 
Igniting  precipitates,  39,  40 
Ihle  and  Rheinhardt,  on  zinc  solution 

for  electrolysis  of  zinc,  212 
Implements  and  tools,  70-74 
Insoluble    mercury    compounds,    an- 
alyzing of,  242 
Iodide  of  potassium  and  starch,  assay 

of  silver  alloy  by,  157,  158 
Iodine,  determination  of  tin  by  means 

of,  230,  231 
lodyrette,  128 
Iridium,  action  of,  on  the  auriferous 

silver  buttons,  177 
separation    of,    from    gold,    by 
D'Hennin's  process  of  fusion, 
178 

Iridosmium  in  gold,  180 
Iron,  auriferous,  168 
filings,  78 

in  nickel  ores,  separation  of,  201 
Lower  Harz  working  assay  of, 

302 
ores,  assay  of  in  large,   unlined 

crucibles,  314 
dry  assay  of,  310-315 
precipitation  of  copper  with,  106- 

108 
pyrites,  276,  277 

as  a  collecting  agent,  79 


TAQUELIN-HUBERT'S  method 
J     for  considerable   percentages   of 

copper,  126,  127 
Jliptner's  fusion   of  gold  and   silver 

alloys,  181 

volumetric   assay   of  gold,    182, 
183 


344 


INDEX. 


T7ANDELHARD   on   the    loss   of 

J\.     gold  in  cupelling,  176 

Kandelhard's  experiments  on  boiling 
argentiferous  gold  in  nitric  acid, 
175 

Karmarsch  on  the  hydrostatic  assay 
of  coins,  160 

Kieselmalachit,  96 

Kiliani  on  electrolytic  assay  of  lead, 

94,  95 
on  electrolytic  assays  of  silver,  160 

Kipp's  apparatus  for  precipitation, 
illustrated  and  described,  37 

Klausenburg's  mining  district,  differ- 
ences allowed  in  assays  of  lead,  89 

Krauss's  process  of  quartation,  182 

Kiistel  on  roasting  gold  ores  contain- 
ing tellurides,  165 

Kiistel' s  assay  of  mercury,  241 


T  AMINATING  the  button  of  gold, 

Jj     173,  174 

Lang's  blast  furnace,  60 

Lead,  81-95 

alloys  of,  wet  assay,  92-95 

and  silver,   addition  of,  in  gold 

assays,  170,  171 
assays,  combined,  138 
argentiferous,  cupellation  of,  138- 

141 

arsenate,  90 
as  a  flux,  78 
assay  by  colorimetric  process 

(Bischof),  94 
of,  by  gravimetric  analysis, 

92-94 
of,   with   potassium  in   clay 

crucibles,  84-85 
of,  with  sulphuric  acid,  89- 

90  ' 

assays    of,    by   electrolytic    pro- 
cesses, 94,  95 
of,  by  volumetric  processes, 

94 

of,  in  the  dry  way,  81-92 
inaccuracy  of,  81 
auriferous,  167 

cupellation  of,  166,  167 
bullion,  dry  assay  of,  143 
carbonate,  81,  90 
chromate,  81,  90,  91 
collecting  silver  with,  129-138 
copper,  and  zinc  in  one  solution, 
determination  of,  221 
,  91 


Lead — 

estimation  of  sulphur  in,  284 
fume,  91 

in  tin,  determination  of,  232 
Lower  Harz  working   assay  of, 

301,  302 
matt,    assaying   of,    in    different 

countries,  83,  84 
Mohr's  process  of  assay,  93 
molybdate  of,  81 
monosulphide  with  foreign  metal- 
lic sulphides,  88 
ore   containing   antimony,   assay 

of,  88 
ores,  81 

examination  of,  for  traces  of 

silver,  141,  142 
oxide,  78,  205 

salts  of,  90-92 
oxides  free  from  earths,  assaying, 

90 

with  earths,  assaying,  90 
oxidizable  nature  of,  99 
phosphate,  90,  91 
quantity  of,  required  for  alloys  of 
gold   with  silver   and  copper, 
169,  170 
separation  of  bismuth  from,  235, 

236 

silicate  (slags),  91,  92 
skimmings,  91 
sulphate,  81,  91 

in  copper,  removal  of,  105 
sulphide,  130 
sweepings,  91 
table  of  multiples  of,  in  assaying 

silver  alloys,  144 
tailings,  91 
various  assays  of,  93 
Lenssen  on  the  volumetric  assay  of 

tin,  231 

Leucopyrite,  251 
Levol  on  lead  assay,  85 
Level's  assay  of  tin  with  potassium 

cyanide,  227,  228 
gas  heating  apparatus,  175 
method  for  manganese  with  iron, 

272,  273 
Linnaeite,  204 
Liquating  fusion,  35 
Liquation,  35 

process  for  determining  antimo- 

nium  crudum,  243 
Litharge,  76,  90,  138 

assay  of  gold  ore  with    nothing 
but,  as  a  flux,  163,  164 


INDEX. 


345 


Litharge — 

entirely  free  from  silver,  prepa- 
ration of,  76 
Litmus  tincture,  80 
Lowe,  assay  of  lead  by,  93 
Lower  Harz,  assay  of  lead  in,  88 

determination  of  silver,  159 
working  assays,  301-303 
Luckow  on  electrolytic  assay  of  zinc. 

213 

Lunge's  method  of  determining  sul- 
phur in  pyrites, 
279,  280 

sources  of  error  in, 
280 


MAGNETIC  iron  pyrites,  276 
pyrites,  188 
Malachite,  96 
Manganese,  264-276 

Belani's  method,  275 

Bunsen's    method    with    iodine, 

270-272 
carbide     preparation     of,    from 

pyrolusite,  264 

electrolytic  assays  of,  275,  276 
gravimetric  assays  of,  266-269 
Hampe's  method,  274,  275 
injurious   influence    of,    on    zinc 
assay  with  potassium  cyanide, 
219 

in  nickel  ores,  treatment  of,  203 
Level's  method  with  iron,   272, 

273 
method  of  Fikentscher-Nolte  for, 

268,  269 
method    of    Fresenius-Will  for, 

267,  268 
methods    of    Bunsen    and   Gay- 

Lussac,  269 
ores,  264 

Volhard's  method,  273,  274 
volumetric  assays  of,  269-275 
Manganic  oxide,  205 
Manganite,  264 
Man»;anous  oxide,  205 
Manipulations,  mechanical,  18-31 
Margueritte's     method    of    assaying 

tungsten,  259 

Mariotte's  bottle,  illustrated,  26,  27 
Mascazzini  and  Parodi  on  the  electro- 
lytic assay  of  zinc,  211 
process  of  electrolytic  assay 

of  lead,  94,  95 
assay  of  lead  by,  93 


Matt,  determination  of  nickel  in,  198 
Matthey  and  Johnson's  new  platinum 

apparatus,  1 75 
May  on  the  electrolytic  assay  of  lead, 

95 
Measuring  and  weighing  samples,  28- 

30 

of  fluxes,  29,  30 
Mechanical  assay  of  gold  by  washing, 

161,  162 

manipulations,  18-31 
Mechernich,  assay  of  lead  matt  in,  84 
Meidinger-Pinkus  battery,  111 
Mercurial  tetrahedrites,  236 
Mercury,  236-242 

assays  of,  at  Almaden,  242 
assays  yielding  free,  237-239 
determination  of,  in  combination 

with  gold,  239-241 
difference   allowed   in  assays  of, 

240 

electrolytic  determination  of,  242 
Eschka's  assay  of,  239-241 
fire  assays  of,  237-241 
gravimetric  assay  of,  241 
Idria,  Austria,  assay  of,  240 
in  silver  alloy,  treatment  of,  151 
Kustel's  assay  of,  241 
native,  236 
ores,  236 

Teuber's  test  for,  240,  241 
volumetric  assays  of,  241,  242 
wet  assays,  241,   242 
Metallic  sulphides,  decomposition  of, 

78 

method  for,  36,  37 
various,     the    quantities    of 
litharge  for  their  decom- 
position, 76 
Metals  for  precipitation  in  wet  assays, 

80 

fusing  points  of,  298-300 
Metric  system,  advantages  of,  in  as- 
saying, 70 
of    weights    and    measures, 

317,  318 
Miargyrite,  128 
Microcosmic  salt,  77 
Millerite,  188 
Mi  Hot  on  electrolytic  determination  of 

zinc,  213 
Mimetene,  90 
Minium,  90 
Mint  cupels,  144,  145 
Mints  at  Brussels  and  Utrecht,  assay 
of  gold  coins  at,  179,  180 


346 


INDEX. 


Mispickel,  251 
Mixing  fusion,  35 

scoops,  illustrated,  30,  31 
Mohr's  assay  of  lead,  93 

burette,  illustrated,  44 

method    of  estimating  arsenious 

acid,  254 

Moisture,  determination  of,  24 
Molybdate  of  lead,  81 
Montana  gold  as§ay  by  washing,  161, 

162 
Moore  on  electrolytic  assay  of  zinc, 

212 
Muffle  furnaces,  45-51 

illustrated,  45 
Munscheid's  gas  blast-furnace,  59 


NAGYAGITE,  161 
Native  arsenic,  251 
copper,  95 

silver  ores,  assay  of,  141 
sulphur,  276 

Neutral  atmosphere,  ignition  in  a,  31 
New  Caledonia  nickel  ores,  assay  of, 

198,  199 

New  York,  assay  of  galena  in,  87 
Nickel,  187-204 

and  cobalt,  difficult   to   separate 

from  copper,  99 
in    nickel     ores,     Donath's 

assay  of,  203,  204 
separation  of,  in  nickel  ores, 

201 

tints  produced  by,  156 
arseniate,  188 
coins,  assay  of,  117,  118 

determining   the  copper  in, 

201,  202 
compounds  containing  antimony, 

treatment  of,  194 
difficult    of    solution,    treat- 
ment of,  1 93,  1 94 
free  from  copoer,  assay  of,  188- 

191 

glance,  188 

in  pyrites  and  matt,  determina- 
tion of,  198 

in  speiss,  electrolytic  determina- 
tion of,  199,  20*0 
ores,  187,  188 

arsenizing,  188,  189 
arsenizing  and  fusion  in  one 

operation,  190 
containing     metallic     sul- 
phides, treatment  of,  188 


Nickel,  ores — 

cupriferous   compounds  rich 
in   copper,  wet   assay  of, 

192 

with  small  percent- 
age of  copper, 
192 

dearsenizing,  191 
Donath's  assay  of  nickel  and 

cobalt  in,  203,  204 
electrolytic  assay  of,  94-197 
free  from   sulphur  and  rich 
in   arsenic,   treatment   of, 
189 
gravimetric    assay    of,    194- 

204 

modifications  which  may  oc- 
cur in  assaying,  189, 
"190 

which  may  occur  in  slag- 
ging off'  the  arsenical 
iron,  191 
New    Caledonia,    assay    of, 

198,  199 

reducing  and  solvent  fusion 
for  collecting  the  metallic 
arsenides,  189 
separation  of  cobalt  in,  203 
of  iron  in,  201 
of  nickel  and  cobalt  in, 

201 
slagging  off  of  the  arsenical 

iron,  190,  191 
the  cobalt  arsenide,  191 
treatment  of,  in  presence  of 
different  metals,  189, 
190 

when  zinc  and  manga- 
nese are  present,  203 
with  iron  filings,  189 
various  assays,  200-204 
volumetric   assay   of  nickel 
and  cobalt  (Do- 
nath),  203,  204 
with     sodium    sul- 
phide, 202,  203 
wet  assay  of,  194-204 

conditions  giving  in- 
accurate results, 
202 

Plattner's  fire  assay,  188 
precipitation  of,  by  zinc,  108 
presence  of  zinc  in,  effect  of,  in 

electrolytic  assays,  197 
protoxide,  205 
silicates,  188 


INDEX. 


347 


Nickel- 
sulphide,  188 
Winkler's  colorimetric  assay  for, 

204 

Nickeliferous  copper,  188 
iron,  188 
pyrrhotine,  193 

solution  from  the  assay  with  sul- 

pho-cyanide    for    determining 

copper  in  nickel  coins,  201,  202 

Nitrate  of  silver,  zinc  assay  with,  220, 

221 
Nitric  acid,  boiling  argentiferous  gold 

in,  174-176 
Non-alloys,  sampling,  18-22 


/"\IL  furnaces  of  Andouin-Deville,  50 

\J         balance,  69 

Organic  combustion  furnaces,  63 

Orsat's  apparatus  for  the  examination 
of  furnace  gases,  291-294 

Oxidized  copper  ores,  96 
ores,  charges  for,  91 
substances  (lead),  90-92 

Oxidizing  agents,  76 
fusion,  34 


"QALLADIUM  passing  into  solution 
£       from  its  alloy  with  gold,  1  78 
Parkes's  assay  of  copper  with  potas- 
sium cyanide,  120-122 
Parodi  and  Mascazzini  on  the  elec- 
trolytic assay  of  zinc,  211 
process  of  electrolytic  assay 

of  lead,  94,  95 
Passaic  zinc,  purity  of,  218 
Patera's  process  for  separating  bismuth 

from  lead,  235,  236 
technical  test  for  uranium,  256 
Pearce's  method  of  determining  arse- 
nic, 254,  255 
simplified  by  Canby, 

255 
Pelouze's  volumetric  assay  of  copper, 

119 
Permanganate,    determining    the 

strength  of  the,  274 
solution,  preparation  of,  183 
Perrot's  furnace,  illustrated  and  de- 
scribed, 54,  55 
gas-muffle  furnace,  illustrated  and 

described,  50,  51 

Phosphate  of  tin,  treatment  of,  127, 
128 


Phosphates  of  copper,  96 
Phosphorus  in  copper,  determination 

of,  127 
Pipettes,  measuring,  illustrated,    42, 

43 

Pitch  blende,  255 

Platiniferous  ores,  assays  of,  185,  186 
fire  assays,  185 
gold  in,  185 
platinum  in,  185 
sand  in,  185 
wet  assay,  185,  186 
Platinum,  184-187 

action  of,  on  the  auriferous  silver 

button,  177 
alloys  of,  186,  187 

electrolytic  assay  of,  187 
dish,  illustrated,  113 
foil,  111 

native,  184,  185 
separation  of,  from  iridium,  187 
of  gold  from,  by  electrolysis, 

183,  184 
spiral,  111 
Plattner's    chlorination    process    for 

gold,  167 

fire  assay  of  nickel,  188 
method  for  the  determination  of 

temperatures,  299 
muffle   furnace,    for    coal,    illus- 
trated and  described,  46-48 
Polybasite,  128 
Potassium  carbonate,  77 

Upper   Harz  assay  of  lead 

with,  87,  88 
cyanide,  75,  78,  80 

assay  of  lead  with,  in  clay 

crucibles,  84,  85 
Parkes's    assay    of    copper 

with,  120-122 
preservation  of  the  solution, 

122 

standardizing,  121 
ferrocyanide,  75,  78 

zinc  assay  with,  218,  219 
iodide,  80 
permanganate,  80 

determination  of  tin  by,  231, 

232 

sulpho-cyanide,  80 
Pourcel's  method  for  chromium,  262 
Precipitates,  drying,  39 

igniting,  39,  40 
Precipitating  fusion,  35 

metals  by  electrolysis,  17 
or  desulphurizing 'agents,  78 


348 


INDEX. 


Precipitation  assay  of  galena,  81,  82 
Debray's  apparatus  for,  illustrated 

and  described,  38 
Kipp's  apparatus  for,  illustrated 

and  described,  37 
of  the  solution,  37 
of  the  sample,  24-28 
Pribrara,  assay  of  galena  at,  86 
Prinsep's  principle  for  the  determi- 
nation of  temperatures,  299 
Protochloride  of  tin,  assay  of  copper 

with,  124,  125 
Psilomelane,  264 
Pulverized  substances,  sampling  of, 

20,  21 

Pulverizing  the  desiccated  mass,  25 
Pulverulent  assay  of  auriferous  silver, 

180-184  * 

sample,  weighing  a,  29 
Pure  silver,  preparation  of,  78,  79 
Purifying  fusion,  35 
Purple  copper  ore,  95 
Pyrargyrite,  128 
Pyrites   and  Matt,  determination   of 

nickel  in,  198 

determination  of  sulphur  in,  279 
poor  in  gold,  164,  165 
waste,  determination  of  sulphur 

in,  281 
Pyrolusite,  264 

assays  of,  264-276 
Pyromorphite,  81,  90,  91 
containing  arsenic,  91 
Pyrostilbite,  243 


QUARTATION,  advantages  in  as- 
saying afforded  by,  182 
of  gold  with  cadmium,   181, 

182 


T)  ASCHETTE'S  furnace,  59 
It  Rammelsbergite,  187,  188 
Kammelsberg  smelting  works,  assay 

at,^88 

Rasping,  samples  by,  19 
Raw  flux,  7.5 
Reagents,  assay,  74-80 

for  decomposing,  31,  32 

for  dry  assays,  74-79 

for  volumetric  wet  assays,  80 

for  wet  assays,  80 
Realgar,  assays  of,  252 

(red  orpiment),  152 
Red  copper,  96 


Red- 
lead  ore,  261 

orpiment  (realgar),  assay  of,  252 
Reducing  agents,  74-76 
fusion,  34,  35 

power,  estimation  of  the,  of  vari- 
ous agents,  75,  76 
processes  for  copper,  various,  1 19 
Refined  slag,  79 
Refining  dishes,  64 
Refractory  ores,  roasting,  33,  34 
Refuse   from    silver    stamping   mills, 

crucible  assay  of,  136,  137 
Remeltincr,  35 
Reodanskite,  188 
Rheinhafdt  and  Ihle  on  zinc  solution 

for  electrolysis  of  zinc,  212 
Rheinsand,  163 

Rhodium,  action  of,   on  the  aurifer- 
ous silver  buttons,  177 
Riche,  assay  of  lead  by,  93 
Richter's  method  of  determining  the 

coking  quality  of  coal,  286 
Ricketts  on  lead  assay,  85 
Roasting,  32,  33 

and  reducing  assay  of  galena,  88, 

89,  94 

dishes,  32,  33,  64 
Robert's  process  for  the  preparation 

of  chemically  pure  gold,  171,  172 
Roessler  on  loss  of  gold  in  cupelling, 

176,  177 

Roessler' s  sinall  furnace  for  the  pro- 
duction of  high  temperatures,  illus- 
trated and  described,  56,  57 
Roll  assay,  drying  and  annealing  of 

the  rolls,  176 
for  argentiferous  gold,  172— 

177 

washing  the  rolls,  1 75,  1 76 
weighing  of  the  rolls,  176 
Rynoso's    assay    for    phosphorus    in 
phosphor  copper,  127  "- 


SALT,  common,  as  a  flux,  79 
of  phosphorus,  77 
Saltpetre,  76,  78 
Salts  of  iron,  nickel,  and  lead,  80 

of  lead  oxide,  90 
Sample,  charging  the,  30,  31 

preparation  "of  the,  24-28 

pulverulent,  weighing  a,  29 
Samples  by  rasping,  19 

for  producing  coins,  23 

from  the  heap,  19 


INDEX. 


349 


Samples — 

sifting,  25-27 

slag,  19 

taken  while  the  ore,  etc.,  is  being 

weighed,  19 
washing,  27,  28 

weighing  and  measuring,  28-30 
Sampling,  18-23 
alloys,  22,  23 
before  weighing,  21 
by  boring,  23 
by  cutting,  22 
by  dipping,  23 
by  dropping  the  ore,  20,  21 
by  granulation,  23 
by  the  cross  method,  1 9,  20 
coins,  22 

goldsmith's  sweepings,  20,  21 
in  some  German  smelting  works, 

21 

of  alloys,  22,  23 

small   ore    and   pulverized    sub- 
stances, 20,  21 
substances  in  a  state  of  fusion, 

21,  22 

in  fragments,  18-20 
while  weighing,  20,  21 
Saxon  assay  of  tin,  223 
Scale,  rough,  69     . 
Schaffner's  assay  of  zinc  as  modified 

by  Brunnlechner,  303-307 
volumetric    assay    of    zinc    with 

sodium  sulphide,  214-218 
Scheibler's  steam  apparatus,  24 
Schemnitz,  differences  allowed  in  as- 
says of  lead,  88 
Schober's  volumetric  assay  for  zinc, 

221 
Schucht  on  electrolytic  assay  of  lead, 

95 
on   electrolytic   assay   of    silver, 

160 

Schulze's   washing    apparatus,    illus- 
trated, 26,  27 
Schwarz's  volumetric  assay  of  copper, 

119 

Scoops,  mixing,  illustrated,  30,  31 
Scorification  assay  for  gold    ores   of 

every  kind,  162 
use  of,  129 
vessels,  64 

Sefstrom's  furnace,  59,  60 
Selenium  in  silver,  determination  of, 

158,  159 

Shef  le's  method  of  assaying  tungsten, 
259 


Sifting  samples,  25-27 
Silver,  128-160 

alloy,  assay  of,  by  iodide  of  po- 
tassium  and   starch,   157, 
158 
Volhard's  assay  with  sulpho- 

cyanide,  155,  156 
alloys,  assay  by  gravimetric  analy- 
sis, 158,  159 
assays  of,  143-160 
dry  assays  of,  143-147 
Gay  Lussac's  assay  of,  with 
sodium  chloride,  148-154 
multiples   of    lead,   used   in 

assaying,  144 

preparation   of    the   normal 
solutions  for  assays  of,  152 
tables   for   determining    the 

fineness  of,  152-154 
volumetric   assays   of,    148- 

158 

wet  assays  for,  147-160 
amalgam,  128 

dry  assay  of,  143 
and  copper  in  one  solution,  de- 
termination of  silver  in,  157 
and  gold  alloys,  with  or  without 

copper,  168-181 
sweepings,  crucible  assay  of, 

135-138 
with    platinum,    cupellation 

of,  186,  187 
lead,  addition  of,  in  gold  assays, 

170,  171 

assay,  combined,  138 
antimonial,  128 
as  a  flux,  78,  79 
auriferous,  pulverulent  assay  of, 

180-184 
Balling's   volumetric    assay   for, 

142,  143 
bromide,  128 

bullion,  various  assays  of,  155 
buttons,  action  of  platinum,  rho- 
dium, and  iridium  on,  177 
charges  for  crucible  assays  of,  in 
various  countries,  135-138 
for  scorification  assay  in  dif- 
ferent localities,  1*33,  134 
chloride  in   copper,  removal   of, 

105 

crucible  assay  of,  134-138 
cupriferous,  assay  of,  144-147 
glance,  128 

in    coins,    hydrostatic    assay  of, 
160 


350 


INDEX. 


Silver- 
electrolytic  determination  of,  1 59, 

160 
examination    of    lead    ores    for 

traces  of,  141,  142 
fire  assays  for,  129-142 
horn,  128 

in  nitric  acid,  dissolving,  175 
iodide,  128 
Lower  Harz,  working  assay  of, 

303 

mint  assay  of,  144 
native,  128 

non-alloys  of,  assays  for,  128-143 
number  of  samples  of,  for  scorifi- 
cation assay,  130 
ore,  brittle,  128 
ores,  native,  assay  of,  141 

principal,  128 
preliminary  assay  of,  144 
pure,  preparation  of,  78,  79 
quantity    of,    absorbed    by    the 

cupel,  146 
ruby,  128 

scorification  assay  of,  129-134 
selenium    in,    determination    of, 

158,  159 
table  of  charges  for  scorification 

assay,  130-132 
telluride  (hessite),  128 
wet  assays,  129,  142,  143 
with  lead,  collecting,  129-138 
with  platinum,  cupellation  of,  186 
Silverware,  refuse  from  the  manufac- 
ture of,  assays  of,  137,  138 
Sire's  assaying  apparatus,  illustrated 

and  described,  149,  150 
Skimmings,  90 

and  dross,  silver,  138 
Slag  samples,  19 
Slags,  lead,  91,  92 

silver,  crucible  assay  of,  136 
Small  ore  and  pulverized  substances, 

sampling  of,  20,  21 
Smalt  assay  of  cobalt,  204-206 
Smaltine,  204 
Smith  and  Knerr  on  the  electrolytic 

determination  of  mercury,  242 
Smithsonite,  207 
Soapstone  crucibles,  65 
Sodium  carbonate,  77 
chloride,  79,  80 

Gay  Lussac's  assay  of  silver 

alloys  with,  148-154 
hyposulphite,  80 
nitroprusside,  80 


Sodium — 

sulphide,  80 

in  an  ammoniacal  solution, 
assay  of  copper  with,  124 
test  of  strength  of,  124 
volumetric   assay    of    nickel 
ore     with,     202, 
203 
of  zinc  with,   214- 

218 

Solution,  empirical,  41 
evaporation  of,  37 
precipitation  of  the,  37 
preparation  of  the  standard,  41, 

42 
Solutions,  decinormal,  41 

normal,  41 

Solvent  agents,  77,  78 
Speiss,  electrolytic    determination   of 
copper,  nickel,  and  cobalt  in,  199, 
200 

Starch  and  iodide  of  potassium,   use 
of,  in  assaying  silver,  157,  158 
paste,  80 

Steel,  auriferous,  168 
Steinbeck's  method  of  assaying  cop- 
per, 122 
Stephanite,  128 
Stibnite,  243 

Stohmann's  siphon  pipette,  43 
Storer,  assay  of  lead  by,  93,  94 
Stromeyerite,  128 
Sublimation  and  distillation,  35 

furnaces  for,  61-63 
furnace,  illustrated  and  described, 

61 

Substances  in  a  state  of  fusion,  samp- 
ling, 21,  22 

in  fragments,  sampling,  18-20 
lead,  oxidized,  90-92 
Sulphide  of  iron,  130 

of  zinc,  130 
Sulphides,   metallic,  method  for,  36, 

37 
Sulphocyanide,  assay  of  copper  with, 

118 

assay  of  silver  alloy  with,  155,  156 
Sulphur,  276-284 

amount  of,,  in  coal  or  its  ash,  287 
assays  by  distillation,  277 

for  the  determination  of  the 
quantity  of,  in  a  substance, 
277-284 

Bodewig's  method  for,  280,  281 
determination  of,  in  pyrites,  py- 
ritous  ores,  etc.,  279 


INDEX. 


351 


Sulphur,  determination  of,  in — 

waste,  281 

Deutoeom's  method  for,  280 
dry   assay,    Hungarian    method, 

278 
(raw    matt    assay)    of, 

277,  278 
earths,  277 
estimation   of  in    metallic   lead, 

284 
gravimetric  assays,  279-281 

determination  of,  in  pyrites, 
according  to  Lunge,  279, 
280 
Lower   Harz  working   assay  of, 

303 

native,  276 
ores,  276 

process    for    determining    small 

quantities  of,  in  materials  and 

products  of  the  iron  works  at 

Creuzot,  279 

volumetric   assay,  Wildenstein's 

method,  282,  283 
assays,  282-284 
determination    of,    in    ores, 

283 

wet  assays,  279-284 
working  test  for  determining  resi- 
due of,  in  roasting  charge  in 
Silesian  zinc  works,  281 
Sulphuretted  copper  ores,  95,  96 
Sulphuric  acid,  accuracy  of  assay  of 

lead  with,  89,  90 
assay  of  lead  with,  89,  90 
Sulphurized  nickel  and  cobalt  ores, 

130 

substances,  81-90 
Sulphurizing  agents,  78 
Swedish  assay,  37 

for  copper,  105 

Sweepings    and    other    refuse    from 
manufactures     of     silverware, 
assaying  of,  137,  138 
goldsmiths',  samples  of,  20,  21 
Sylvanite,  161 


TABLE   for   determining  the  fine- 
ness of  silver  alloys,  152-154 
Tabular  synopses,  297-301 
Talbott's  method  of  separating  tung- 
sten from  tin,  260 

Tarnowitz,  assay  of  lead  matt  in,  83 

Taylor,    Charles,   on  heat   regulator, 

rU.  S.  Assay  Office,  N.  Y.,  309. 


Tellerium,  white,  161 
Tellurides  in  gold  ores,  165,  166 
Tenny    on   the   electrolytic   assay  of 

lead,  95 

Tetradymite,  233 
Tetrahedrite,  95 

Teuber's  test  for  mercury,  240,  241 
Thermostats,  24 
Tin,  223-233 

assays,  accurate  results  obtained, 

231 

comparative  accuracy  of  German 
and  English  or  Cornish  assays 
of,  224 

Cornish  assay  of,  227 
determination   of,   by   means   of 
potassium   permanganate, 
231,  232 

of,  by  iodine,  230,  231 
of  lead  in,  232 
electrolytic  determination  of,  233, 

234 
fire  assays  for,  224-229 

*  of  object  of,  224 
German  assay  of,  224 
gravimetric  assays  of,  228-239 
in  copper,  removal  of,  105 

separation  of.  99 
in  presence  of  antimony,  detec- 
tion of,  232 
in  separate  grains,  treatment  of, 

226,  227 

in  silver  alloy,  treatment  of,  151 
in   tin    slags,    determination   of, 

229,  230 
Level's  assay  of,  with  potassium 

cyanide,  227,  228 
losses  of,  by  German  and  Cornish 

methods,  224 
ore,  slagging  off  of,  226 
ores,  223 

with  foreign  metallic  sul- 
phides, arsenides,  and  an- 
timonides,  treatment  of, 
225,  226 

with    many   earthy    admix- 
tures, assay  of,  225 
oxide,  reducing,  224 
Saxon  assay  of,  223 
slags,  treatment  of,  229,  230 
volumetric  assays,  230-232 
wet  assay  of,  228-233 
Tincture  of  Brazil  wood,  80 
Tinstone,  223 

and  metals  in  combination  with, 
specific  gravities  of,  225 


352 


INDEX. 


Tinstone — 

determination    of,    by    washing, 

223,  224 
digestion  of,  with  aqua  regia,  228, 

229 

Tookey,  use  of  platinum  tube  by,  175 
Tools  and  implements,  70-74 
Torry  and  Eaton  on  effect  of  other 
metals    in    assay    of    copper, 

120 

H.  G.,  on  heat  regulator,  U.  S. 
Assay  Office,  N.  Y.,  307- 
309 

Touchstone,  examination  of  gold  al- 
loys on  the,  169 
Toughening  of  brittle  gold,  184 
Tungsten,  258-261 

Berzelius's  method  of  assaying, 

259 
Cobenzl's   method   of   assaying, 

260 

fire  assay  of,  259 
gravimetric  assays,  259,  260 
Margueritte's  method   of  assay- 
ing, 259 

preparation  of  the  titrating  solu- 
tion for,  261 
separation  from  tin,  260 
Sheele's  method  of  assaying,  259 
volumetric  assay  of,  261 
wet  assays,  259-261 
Zettner's  method  of  volumetric 
assay  of,  261 


TTLLMANITE,  188 

U      Upper  Harz,  assay  of  galena  in, 

^1,  82,  87 
with  potassium  car- 
bonate in,  87,  88 
Uranium,  255-258 

analytical  process  for,  255 
determination  of  with  potassium 

dichromate  and  iodine,  258 
difficulty  of  determining  oxysalts 

of,  257 

gravimetric  assays  of,  255-257 
ores,  255 

Patera's  technical  test,  256 
precipitation   of,   in  presence  of 

alkaline  earths,  256,  257 
separation  from  calcium,  256 
volumetric  assay  of,  257 
wet  assays  of,  255-258 
Utrecht,  mint  of,  assaying  gold  coins 
at,  179,  180 


VALENTINITE,  243 
Vanning,  art  of,  28 

shovel,  illustrated,  27 
Van  Riemsdijk  on  cupelling  pure  gold, 

178,  179 
Varvicite,  264 
Vessels,  assay,  63-69 

for  the  dry  method,  63-68 
for  the  wet  method,  68,  69 
of  bone  ash,  66-68 
Vitriol,  blue,  96 
Volatilizing  fluxes,  79 
Volhard's  method  for  manganese.  273, 

274 
Volhard's  volumetric  assay  of  copper, 

119 
Volumetric  analysis,  17 

assays  by,  40-45 
vessels  for,  68 
assay  of  gold,  182,  183 
assays,  advantages  of,  18 

for  copper,  104 
wet  assays,  reagents  for,  80 


WAD,  264 
Wait's    machine    for    making 

cupels,  illustrated,  67,  68 
Wales,  assay  of  lead  matt  in,  84 
Wash-bottle,  illustrated,  38 
Washing  apparatus,  Schulze's,  26,  27 

samples,  27,  28 
Water-bath,  illustrated,  24 
Weighing  alloys,  29 

and  measuring  samples,  28-30 
a  pulverulent  sample,  29 
fluxes,  29 

hygroscopic  substances,  29 
the  button,  29 
Weights  and  balances,  69,  70 

measures     (English),     319, 

320 

Weil's  method  of  volumetric  determi- 
nation of  sulphur  in  ores,  283 
Welch's  furnace,  59 
Welter's  law,  288 
Wernicke    on    electrolytic    assay    of 

lead,  95 
Wet  assay,  1  7 

assays  of  copper,  1 04-1 28 

'reagents  for,  80 

method,  operations  by  the,  35-45 
White  flux,  75 

tellurium,  161 

WhitteH,  Dr.  A.  P.,  humid  assay  for 
silver,  155  v 


INDEX. 


Wiessnegg's  gas  furnace,  56 

Wildenstein's  volumetric  assay  of  sul- 
phur, 282,  283 

Willemite,  207 

AVind  furnaces  for  free  burning  coal,  55 
for  illuminating  gas,  55 

AVinkler's  proposed  colorimetric  assay 
for  nickel,  204 

Wolfram,  258 

AVrought-iron  vessels,  65,  66 

Wulfenite,  81,  90,  91 


YELLOW  lead  ore,  90,  91 
orpiment,  artificial,  252 
assays  of,  252 
native,  252 

Yver,  on  separation  of  zinc  and  cad 
mium,  222 


FTETTNER'S  method  of  the  volu- 
/J     metric  assay  of  tungsten,  261 
Zimmermann's  method  of  determin- 
ing uranium,  258 
Zinc,  207,  221 

and  cadmium,  separation  of,  222 
and   manganese   in   nickel   ores, 

203 

assay,  admixtures  having  a  dis- 
turbing  effect,   to  be   re- 
moved, 217 
coloration   of  the   hydrated 

ferric  oxide  in,  216 
preparation  of  the  titrating 

solutions,  220 
quantity  of  fluid  to  be  used 

in  Schaffner's  assay,  216 
quantity  of  hydrated  ferric 

acid  in,  216 

Schaffner's,  points  to  be  ob- 
served in,  216 
uniform  light  requisite  during 

the  titration,  218 
with   potassium   ferro-cyan- 

ide,  218,  219 

assays,  indicators  for  final  reac- 
tion, 215,  216 
as  zinc  oxide,  determination  of, 

210 

blende,  207,  208 
bloom,  207 
carbonate,  207 
combined  with  sulphur,  assay  for, 

220,  221 

commercial,  purification  of,  218 
23 


Zinc- 
copper,  and  lead  in  one  solution, 

determination  of,  221 
determination   of,    as    zinc    sul- 
phide, 209,  210 
by  decomposing  the  sulphide 
of  zinc  with   chloride  of 
silver,  and  determining  the 
zinc  from  the  equivalent 
content  of  chlorine,  219, 
220 

from   its  combinations  with 

sulphur  by  decomposition 

with  nitrate  of  silver,  220, 

221 

dissolving  of,  with  hydrochloric 

acid,  108 

distillation  assay,  207,  208 
dry  assays,  207-209 
electrolytic    assay   of,    according 
to  Beilstein  and  Jawein,   210, 
211 
for  fixing  the  standard  solution, 

218 

free  from  lead  and  arsenic,  pre- 
cipitation of  copper  with,  107, 
108 

granulated,  108 
granulation  of,  80 
gravimetric  assays,  209-214 
in  a  slightly  acid  solution  in  the 
presence  of  a  strong  mineral 
acid,  determination  of,  213,  214 
in  copper,  separation  of,  99 
indirect  assay,  208,  209 
in   ores,   electrolytic   method   of 

determining,  213 
in  presence  of  copper,  precipita- 
tion of,  214,  215 
of  metals  soluble  in  ammo- 
nia, assays  for,  214,  215 
Lower  Harz  working  assay  of, 

302 

ore,  electrolytic  assay,  210-214 
removal   of   various    metals 

from,  217,  218 
when  copper  is  present,  assay 

for,  211 
ores,  207 

oxide,  determination  of,  210 
precipitation  of,  by  various  pro- 
cesses, 212,  213 
from   its    sulphate   solution, 

211 

Schaffner's  volumetric  assay  with 
sodium  sulphide,  214-218 


354 


INDEX. 


Zinc — 

Schober's  volumetric   assay  for, 

221 

silicate,  207 
sulphate    solution,    precipitation 

of  zinc  from,  211,  212 


Zinc- 
sulphide,  determination  of,   209, 

210 

volumetric  assays,  214-221 
wet  assays,  209-221 

Zinkite,  207* 


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BRANNT.— A  Practical  Treatise  on  the  Raw  Materials  and  the 
Distillation  and  Rectification  of  Alcohol,  and  the  Prepara- 
tion of  Alcoholic  Liquors',  Liqueurs,  Cordials,  Bitters,  etc.: 
Edited  chiefly  from  the  German  ol  Dr.  K.  Stammer,  J)r.  F.  Eisner, 
and  E.  Schubert.     By  WM.  T.  BRANNT.     Illustrated  by  thirty-one 
engravings.     I2ino. $>2>$Q 


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BRANNT— WAHL.— The  Techno- Chemical  Receipt  Book: 

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portant,  and  most  useful  discoveries  in  Chemical  Technology,  anc 
their  Practical  Application  in  the  Arts  and  the  Industries.  Editec 
chiefly  from  the  German  of  Drs.  Winckler,  Eisner,  Heintze,  Mier 
zinski,  Jacohsen,  Koller,  and  Heinzerling,  with  additions  by  WM.  1. 
BRANNT  and  WM.  H.  WAHL,  PH.  D.  Illustrated  by  78  engravings. 
I2mo.  495  pages  .  ...  $2.00 

BROWN.— Five  Hundred  and  Seven  Mechanical  Movements: 
Embracing  all  those  which  are  most  important  in  Dynamics,  Hy- 
draulics, Hydrostatics,  Pneumatics,  Steam-Engines,  Mill  and  other 
Gearing,  Presses,  Horology  and  Miscellaneous  Machinery;  and  in- 
cluding many  movements  never  before  published,  and  several  of 
which  have  only  recently  come  into  use.  By  HENRY  T.  BROWN 
I2mo. $1.00 

BUCKMASTER.— The  Elements  of  Mechanical  Physics  : 
By  J.  C.   BUCKMASTER.       Illustrated    with    numerous   engravings. 
I2mo.         .          .         .         .          .         .          .         ...         $l.oo 

BULLOCK.— The  American  Cottage  Builder  : 

A  Series  of  Designs,  Plans  and  Specifications,  from  $200  to  $20,000, 
for  Homes  for  the  People ;  together  with  Warming,  Ventilation, 
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Architect  and  Editor  of  "  The  Rudiments  of  Architecture  and 
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BULLOCK. — The  Rudiments  of  Architecture  and  Building: 
For  the  use  of  Architects,  Builders,   Draughtsmen,  Machinists,  En- 
gineers and  Mechanics.     Edited  by  JOHN  BULLOCK,  author  of  "  The 
American  Cottage  Builder."   Illustrated  by  250  Engravings.  8vo.  $3.00 

BURGH.— Practical    Rules    for    the    Proportions   of     Modern 

Engines  and  Boilers  for  Land  and  Marine  Purposes. 
By  N.  P.  BURGH,  Engineer.     I2mo.          ,      •  .      •"••.-       »        $i-$Q 

BYLES.— Sophisms    of     Free    Trade    and    Popular    Political 

Economy  Examined. 

By  a  BARRISTER  (SIR  JOHN  BARNARD  BYLES,  Judge  of  Common 
Pleas).  From  the  Ninth  English  Edition,  as  published  by  ihe 
Manchester  Reciprocity  Association.  I2mo.  .  .  .  $1-25 

BOWMAN.— The  Structure  of  the  Wool  Fibre  in  its  Relation 

to  the  Use  of  Wool  for  Technical  Purposes : 
Being  the  substance,  with  additions,  of  Five  Lectures,  delivered  at 
the  request  of  the  Council,  to  the  members  of  the  Bradford  Technical 
College,  and  the  Society  of  Dyers  and  Coloiists.  By  F.  H.  Low- 
MAN,  D.  Sc.,  F.  R.  S.  K,  F.  L.  S.  Illustrated  by  32  engravings. 
8vo.  .  .  .  .  .  •  .  .  .  .  $5.50 

BYRNE. — Hand-Book  for  the  Artisan,  Mechanic,  and  Engi- 
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Comprising  the  Grinding  and  Sharpening  of  Cutting  Tools,  Abvc-.  ,-e 
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HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 


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BYRNE. — Pocket-Book  for  Railroad  and  Civil  Engineers: 
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work;  Levelling;  the  Calculation  of  Cuttings;  Embankments;  Earth- 
work, etc.  By  OLIVER  BYRNE.  i8mo.,  full  bound,  pocket-book 
form |li. 75 

BYRNE.— The  Practical  Metal- Worker's  Assistant :  I 

Comprising  Metallurgic  Chemistry ;  the  Arts  of  Working  all  Metal$ 
and  Alloys  ;  Forging  of  Iron  and  Steel ;  Hardening  and  Tempering; 
Melting  and  Mixing;  Casting  and  Founding ;  Works  in  Sheet  Metal; 
the  Processes  Dependent  on  the  Ductility  of  the  Metals;  Soldering; 
and  the  most  Improved  Processes  and  Tools  employed  by  Metal- 
workers. With  the  Application  of  the  Art  of  Electro- Metallurgy  to 
Manufacturing  Processes ;  collected  from  Original  Sources,  and  from 
the  works  of  Holtzapffel,  Bergeron,  Leupold,  Piumier,  Napier, 
Scoffern,  Clay,  Fairbairn  and  others.  By  OLIVER  BYRNE.  A  new, 
revised  and  improved  edition,  to  which  is  added  an  Appendix,  con- 
taining The  Manufacture  of  Russian  Sheet- Iron.  By  JOHN  PERCY, 
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Branch  of  the  Subject.  8vo $5-OO 

BYRNE.— The  Practical  Model  Calculator: 

For  the  Engineer,  Mechanic,  Manufacturer  of  Engine  Work,  Nava* 
Architect,  Miner  and  Millwright.  By  OLIVER  BYRNE.  8vo.,  nearly 
600  paijes #3  oo 

CABINET  MAKER'S  ALBUM  OF  FURNITURE : 
Comprising  a  Collection  of  Designs  for  various  Styles  of  Furniture. 
Illustrated  by  Forty-eight   Large  and  Beautifully  Engraved   Plates. 
Oblong,  8vo $2.00 

CALLINGHAM.— Sign  Writing  and  Glass  Embossing: 

A  Complete  Practical  Illustrated  Manual  of  the  Art.  By  JAMES 
CALLINGHAM.  i2mo $1.50 

CAMPIN. — A  Practical  Treatise  on  Mechanical  Engineering: 
Comprising  Metallurgy,  Moulding,  Casting,  Forging,  Tools,  Work, 
shop  Machinery,  Mechanical  Manipulation,  Manufacture  of  Steanv 
Engines,  etc.  With  an  Appendix  on  the  Analysis  of  Iron  and  Iron 
Ores.  By  FP  ANCIS  CAMPIN,  C.  E.  To  which  are  added,  Observations 
on  the  Construction  of  Steam  Boilers,  and  Remarks  upon  Furnaces 
used  for  Smoke  Prevention ;  with  a  Chapter  on  Explosions.  By  R. 
ARMSTRONG,  C.  E.,  and  JOHN  BOURNE.  Rules  for  Calculating  th« 
Change  Wheels  for  Screws  on  a  Turning  Lathe,  and  for  a  Wheel^ 
cutting  Machine.  By  J.  LA  NICCA.  Management  of  Steel,  Includ- 
ing Forging,  Hardening,  Tempering,  Annealing,  Shrinking  and 
Expansi  >n  ;  and  the  Case-hardening  of  Iron.  By  G.  EDE.  8vo. 
Illustrated  with  twenty-nine  plates  and  100  wood  engravings  $5.00 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 


CAREY.— A  Memoir  of  Henry  C.  Carey. 
By  DR.  WM.  ELDER.    With  a  portrait.     8vo.,  cloth         .         .        75 

CAREY.— The  Works  of  Henry  C.  Carey : 

Harmony  of  Interests  :    Agricultural,  Manufacturing  and  Commer. 

cial.     8vo.  .         .         $1.25 

Manual  of  Social  Science.  Condensed  from  Carey's  "  Principles 
of  Social  Science."  By  KATE  McKEAN.  I  vol.  I2mo.  .  $2.00 
Miscellaneous  Works.  With  a  Portrait.  2  vols.  8vo.  £10.00 

Past,  Present  and  Future.     8vo $2.50 

Principles  of  Social  Science.  3  volumes,  8vo.  .  .  $7.50 
The  Slave-Trade,  Domestic  and  Foreign ;  Why  it  Exists,  and 
How  it  may  be  Extinguished  (1853).  8vo.  .  .  .  $2.00 
The  Unity  of  Law :  As  Exhibited  in  the  Relations  of  Physical, 
Social,  Mental  and  Moral  Science  (1872).  8vo.  .  .  $2.50 

CLARK. — Tramways,  their  Construction  and  Working : 

Embracing  a  Comprehensive  History  of  the  System.  With  an  ex- 
haustive analysis  of  the  various  modes  of  traction,  including  horse- 
power, steam,  heated  water  and  compressed  air;  a  description  of  the 
varieties  of  Rolling  stock,  and  ample  details  of  cost  and  working  ex- 
penses. By  D.  KINNEAR  CLARK.  Illustrated  by  over  200  wood 
engravings,  and  thirteen  folding  plates.  I  vol.  8vo.  .  $9.00 

COLBURN. — The  Locomotive  Engine  : 

Including  a  Description  of  its  Structure,  Rules  for  Estimating  its 
Capabilities,  and  Practical  Observations  on  its  Construction  and  Man- 
agement. By  ZERAH  COLBURN.  Illustrated.  12010.  .  $1.00 

COLLENS. — The  Eden  of  Labor ;  or,  the  Christian  Utopia. 
By  T.  WHARTON  COLLENS,  author  of  "  Humanics,"    "The  History 
of  Charity,"  etc.     I2mo.     Paper  cover,  $  I.  oo;  Cloth          .         $1.25 

3OOLEY. — A  Complete  Practical  Treatise  on  Perfutnery : 
Being  a  Hand-book  of  Perfumes,  Cosmetics  and  other  Toilet  Articles, 
With   a  Comprehensive    Collection  of  Formulae.     By   ARNOLD   J. 
COOLEY.    I2mo.         .         .         .  •      v         »  :_:'  «         .         .         $i.5d 

COOPER. — A  Treatise  on  the  use  of  Belting  for  tfie  Trans- 
mission of  Power. 

With  numerous  illustrations  of  approved  and  actual  methods  of  ar- 
ranging Main  Driving  and  Quarter  Twist  Belts,  and  of  Relt  Fasten 
ings.  Examples  and  Rules  in  great  number  for  exhibiting  and  cal- 
culating the  size  and  driving  power  of  Belts.  Plain,  Particular  and 
Practical  Directions  for  the  Treatment,  Care  and  Manigement  of 
Belts.  Descriptions  of  many  varieties  of  Beltings,  together  witn 
chapters  on  the  Transmission  of  Power  by  Ropes;  by  Iron  and 
Wood  Frictional  Gearing;  on  the  Strength  of  Belting  Leather;  and 
on  the  Experimental  Investigations  of  Morin,  Briggs,  and  others.  By 
JOHN  H.  COOPER,  M.  E.  8vo #3.50 

CRAIK.— The  Practical  American  Millwright  and  M'Uer. 
By  DAVID  CRAIK,  Millwright.     Illustrated  by  numerous  wood  en- 
gravings and  two  folding  plates.     8vo $3.50 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.  9 

CROSS. — The  Cotton  Yarn  Spinner: 

Showing  how  the  Preparation  should  be  arranged  for  Different 
Counts  of  Yarns  by  a  System  more  uniform  than  has  hitherto  been 
practiced;  by  having  a  Standard  Schedule  from  which  we  make  all 
our  Changes.  By  RICHARD  CROSS.  122  pp.  I2mo.  .  75 

CRISTIANI. — A  Technical  Treatise  on  Soap  and  Candles: 
With  a  Glance  at  the  Industry  of  Fats  and  Oils.     By  R.  S.  CRIS- 
TIANI, Chemist.     Author  of  "  Perfumery  and  Kindred  Arts."     Illus- 
trated by  176  engravings.     581  pages,  8vo.         .         .         .      $15.00 

COAL  AND  METAL  MINERS'  POCKET  BOOK: 

Of  Principles,  Rules,  Formulae,  and  Tables,  Specially  Compiled 
and  Prepared  for  the  Convenient  Use  of  Mine  Officials,  Mining  En- 
gineers, and  Students  preparing  themselves  for  Certificates  of  Compe- 
tency as  Mine  Inspectors  or  Mine  Foremen.  Revised  and  Enlarged 
edition.  Illustrated,  565  pages,  small  I2mo  ,  cloth.  .  $2.00 

Pocket  book  form,  flexible  leather  with  flap  .         .  $2.75 

DAVIDSON. — A  Practical  Manual  of  House  Painting,  Grain- 
ing, Marbling,  and  Sign- Writing: 

Containing  full  information  on  the  processes  of  House  Painting  in 
Oil  and  Distemper,  the  Formation  of  Letters  and  Practice  of  Sign- 
Writing,  the  Principles  of  Decorative  Art,  a  Course  of  Elementary 
Drawing  for  House  Painters,  Writers,  etc.,  and  a  Collection  of  Useful 
Receipts.  With  nine  colored  illustrations  of  \Voods  and  Marbles, 
and  numerous  wood  engravings.  By  ELLIS  A,  DAVIDSON.  i2tno. 

$300 

DAVIES. — A  Treatise  on  Earthy  and  Other    Minerals   and 

Mining: 

By  D.  C.  DAVIES,  F.  G.  S.,  Mining  Engineer,  etc.  Illustrated  by 
76  Engravings.  I2mo. #5  OO 

DAVIES. — A  Treatise  on  Metalliferous  Minerals  and  Mining: 
By  D.  C.  DAVIKS,  F.  G.  S  ,  Mining  Engineer,  Examiner  of  Mines, 
Quarries  and  Collieries.  Illustrated  by  148  engravings  of  Geological 
Formations,  Mining  Operations  and  Machineiy,  drawn  from  the 
practice  of  all  parts  of  the  world.  Fifth  Edition,  thoroughly  Revised 
and  much  Enlarged  by  his  son,-  E.  Henry  Davies.  I2mo ,  524 
pages  .......  .  $5-°° 

DAVIES. — A  Treatise  on  Slate  and  Slate  Quarrying: 

Scientific.  Practical  and  Commercial.  By  D  C.  DAVits,  F.  G  S., 
Mining  Engineer,  etc.  Writh  numerous  illustrations  and  folding 
plates.  I2mo $2.00 

DAVIS. — A  Practical  Treatise  on  the  Manufacture  of  Brick, 

Tiles  and  Terra- Cotta: 

Including  Stiff  Chy,  Dry  Clay,  Hand  Made.  Pressed  or  Front,  and 
Roadway  Paving  Brick,  Enamelled  Brick,  with  Glazes  and  Colors, 
Fire  Brick  and  Blocks,  Silica  Brick,  Carbon  Brick,  Glass  Pots,  Re- 


10         HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

torts,  Architectural  Terra-Cotta,  Sewer  Pipe,  Drain  Tile,  Glazed  and 
Unglazed  Roofing  Tile,  Art  Tile,  Mosaics,  and  Imitation  of  Intarsia 
or  Inlaid  Surfaces.  Comprising  every  product  of  Clay  employed  in 
Architecture,  Engineering,  and  the  Blast  Furnace.  With  a  Detailed 
Description  of  the  Different  Clays  employed,  the  Most  Modern 
Machinery,  Tools,  and  Kilns  used,  and  the  Processes  for  Handling, 
Disintegrating,  Tempering,  and  Moulding  the  Clay  into  Shape,  Dry- 
ing, Setting,  and  Burning.  By  Charles  Thomas  Davis.  Third  Edi- 
tion. Revised  and  in  great  part  rewritten.  Illustrated  by  261 
engravings.  662  pages  .  .  .  .  '•  .  .  $5-°° 

DAVIS. — A  Treatise  on  Steam-Boiler  Incrustation  and  Meth- 
ods for  Preventing  Corrosion  and  the  Formation  of  Scale: 
By  CHARLES  T.  DAVIS.     Illustrated  by  65  engravings.     8vo.    $1.50 

DAVIS. — The  Manufacture  of  Paper: 

Being  a  Description  of  the  various  Processes  for  the  Fabrication, 
Coloring  and  Finishing  of  every  kind  of  Paper,  Including  the  Dif- 
ferent Raw  Materials  and  the  Methods  for  Determining  their  Values, 
the  Tools,  Machines  and  Practical  Details  connected  with  an  intelli- 
gent and  a  profitable  prosecution  of  the  art,  with  special  reference  to 
the  best  American  Practice.  To  which  are  added  a  History  of  Pa- 
'per,  complete  Lists  of  Paper-Making  Materials,  List  of  American 
Machines,  Tools  and  Processes  used  in  treating  the  Raw  Materials, 
and  in  Making,  Coloring  and  Finishing  Paper.  By  CHARLES  T. 
DAVIS.  Illustrated  by  156  engravings.  608  pages,  8vo.  #6.00 

DAVIS.— The  Manufacture  of  Leather: 

Being  a  description  of  all  of  tl  Processes  for  the  Tanning,  Tawing, 
Currying,  Finishing  and  Dyeing  of  every  kind  of  Leather ;  including 
the  various  Raw  Materials  and  the  Methods  for  Determining  their 
Values;  the  Tools,  Machines,  and  all  Details  of  Importance  con- 
nected with  an  Intelligent  an-d  Profitable  Prosecution  of  the  Art,  with 
Special  Reference  to  the  Best  American  Practice.  To  which  are 
added  Complete  Lists  of  all  American  Patents  for  Materials,  Pro- 
cesses, Tools,  and  Machines  for  Tanning,  Currying,  etc.  By  CHARLES 
THOMAS  DAVIS.  Illustrated  by  302  engravings  and  12  Samples  of 
Dyed  Leathers.  One  vol.,  8vo.,  824  pages  .  .  .  $25.00 

DAWIDOWSKY— BRANNT.— A  Practical  Treatise  on  the 
Raw  Materials  and  Fabrication  of  Glue,  Gelatine,  Gelatine 
Veneers  and  Foils,  Isinglass,  Cements,  Pastes,  Mucilages, 
etc.: 

Based  upon  Actual  Experience.  By  F.  DAWIDOWSKY,  Technical 
Chemist.  Translated  from  the  German,  with  extensive  additions, 
including  a  description  of  the  most  Recent  American  Processes,  by 
WILLIAM  T.  BRANNT,  Graduate  of  the  Royal  Agricultural  College 
of  Eldena,  Prussia.  35  Engravings.  I2mo.  .  .  .  $2.50 

DE  GRAFF. — The  Geometrical  Stair-Builders*  Guide : 
Being  a  Plain  Practical  System  of  Hand-Railing,  embracing  all  ita 
necessary  Details,  and  Geometrically  Illustrated  by  twenty-two  SteeJ 
Engravings ;  together  with  the  use  of  the  most  approved  principle! 
of  Practical  Geometry.     By  SIMON  DE  GRAFF,  Architect.      410. 

I2.SO 


HENRY   CAREY   BAIRD   &   CO.'S   CATALOGUE:.        n 

DE  KONINCK— DIETZ.— A  Practical  Manual  of  Chemical 

Analysis  and  Assaying : 

As  applied  to  the  Manufacture  of  Iron  from  its  Ores,  and  to  Cast  Iron, 
Wrought  Iron,  and  Steel,  as  found  in  Commerce.  By  L.  L.  DH 
KONINCK,  Dr.  Sc.,  and  E.  DIETZ,  Engineer.  Edited  with  Notes,  by 
ROBERT  MALLET,  F.  R.  S.,  F.  S.  G.,  M.  I.  C.  E.,  etc.  American 
Edition,  Edited  wilh  Notes  and  an  Appendix  on  Iron  Ores,  by  A.  A. 
FESQUET,  Chemist  and  Engineer.  I2mo.  .  .  .  $1.50 

DUNCAN.— Practical  Surveyor's  Guide: 

Containing  the  necessary  information  to  make  any  person  of  corm 
mon  capacity,  a  finished  land  surveyor  without  the  aid  of  a  teacher 
By  ANDREW  DUNCAN.  Revised.  72  engravings,  214 pp.  I2mo.  $1.50 

DUPLAIS. — A  Treatise  on  the  Manufacture  and  Distillation 

of  Alcoholic  Liquors : 

Comprising  Accurate  and  Complete  Details  in  Regard  to  Alcohol 
from  Wine,  Molasses,  Beets,  Grnin,  Rice,  Potatoes,  Sorghum,  Aspho 
del,  Fruits,  etc. ;  with  the  Di>tillat'on  and  Rectification  of  Brandy. 
Whiskey,  Rum,  Gin,  Swiss  Absinthe,  etc.,  the  Preparation  of  Aro- 
matic Waters,  Volatile  Oils  or  Essences,  Sugnrs,  Syrups,  Aromatic 
Tinctures,  Liqueurs,  Cordial  Wines,  Effervescing  Wines,  etc.,  the 
Ageing  of  Brandy  and  the  improvement  of  Spirits,  with  Copiona 
Directions  and  Tables  for  Testing  and  Reducing  Spirituous  Liquors, 
etc.,  etc.  Translated  and  Edited  from  the  French  of  MM.  DUPLAIS, 
Aine  et  Jeune.  By  M.  McKENNiE,  M.  D.  To  which  are  added  the 
United  States  Internal  Revenue  Regulations  for  the  Assessment  and 
Collection  of  Taxes  on  Distilled  Spirits.  Illustrated  by  fourteen 
folding  plates  and  several  wood  engravings.  743  pp.  8vo.  $10  oo 

DUSSAUCE. — Practical  Treatise  on  the  Fabrication  of  Matches, 

Gun  Cotton,  and  Fulminating  Powder. 
By  Professor  H.  DUSSAUCE.     I2mo.     -    .     '    .         .         .         $300 

DYER  AND  COLOR-MAKER'S  COMPANION: 

Containing  upwards  of  two  hundred  Receipts  for  making  Colors,  on 
the  most  approved  principles,  for  all  the  various  styles  and  fabrics  now 
in  existence;  with  the  Scouring  Process,  and  plain  Directions  for 
Preparing,  Washing-off,  and  Finishing  the  Goods.  I2mo.  $1.00 

EDWARDS. — A  Catechism  of  the  Marine  Steam-Engine, 
For  the  use  of  Engineers,  Firemen,  and  Mechanics.  A  Practical 
Work  for  Practical  Men.  By  EMORY  EDWARDS,  Mechanical  Engi- 
neer. Illustrated  by  sixty-three  Engravings,  including  examples  of 
the  most  modern  Engines.  Third  edition,  thoroughly  revised,  with 
much  additional  matter.  12  mo.  414  pages  .  .  .  $2  oo 

EDWARDS. — Modern  American  Locomotive  Engines, 
Their  Design,  Construction  and  Management.     By  EMORY  EDWARDS, 
Illustrated  I2mo #2.00 

EDWARDS.— The  American  Steam  Engineer: 

Theoretical  and  Practical,  with  examples  of  the  latest  and  most  ap- 
proved American  practice  in  the  design  and  construction  of  Steam 
Engines  and  Boilers.  For  the  use  of  engineers,  machinists,  boiler- 
m«\kers,  and  engineering  students.  By  EMORY  EDWARDS.  Fully 
illustrated,  419  pages.  I2mo.  ....  £2.50 


12         HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

EDWARDS. — Modern  American  Marine  Engines,  Boilers,  an! 
Screw  Propellers, 

Their  Design  and  Construction.  Showing  the  Present  Practice  ot 
the  most  Eminent  Engineers  and  Marine  Engine  Buildeis  in  the 
United  States.  Illustrated  by  30  large  and  elaborate  plates.  410.  $5.0x1 
CDWARDS.— The  Practical  Steam  Engineer's  Guide 
In  the  Design,  Construction,  and  Management  of  American  Stationary, 
Portable,  and  Steam  Fire- Engines,  Steam  Pumps,  Boilers.  Injector^ 
Governors,  Indicators,  Pistons  and  Rings,  Safety  Valves  and  Steam 
Gauges.  For  the  use  of  Engineers,  Firemen,  and  Steam  Users.  By 
EMORY  EDWARDS.  Illustrated,  by  119  engravings.  A2O  pages. 

I2111O.         .  .  .        "    .  .  .  .  .  .  .  $2    50 

EISSLER.— The  Metallurgy  of  Gold  : 

A  Practical  Treatise  on  the  Metallurgical  Treatment  of  Gold-Bear- 
ing  Ores,  including  the  Processes  of  Concentration  and  Chlorination, 
and  the  Assaying,  Melting,  and  Refining  of  Gold.  By  M.  EISSLER. 
With  132  Illustrations.  I2ino. $5.00 

EISSLER.— The  Metallurgy  of  Silver  : 

A  Practical  Treatise  on  the  Amalgamation,  Roasting,  and  Lixiviation 
of  Silver  Ores,  including  the  Assaying,  Melting,  and  Refining  of 
Silver  Bullion.  By  M.  EISSLER.  124  Illustrations.  336  pp. 
I2mo $4-25 

ELDER. — Conversations  on  the  Principal  Subjects  of  Political 

Economy. 
By  DR.  WILLIAM  ELDER.     8vo $2 .50 

ELDER. — Questions  of  the  Day, 

Economic  and  Social.     By  DR.  WILLIAM  ELDER.     8vo.     .      $3.00 

ERNI. — Mineralogy  Simplified. 

Easy  Methods  of  Determining  and  Classifying  Minerals,  including 
Ores,  by  means  of  the  Blow]  ipe,  and  by  Humid  Chemical  Analysis, 
based  on  Professor  von  Kobell's  Tables  for  the  Determination  of 
Minerals,  with  an  Introduction  to  Modern  Chemistry.  By  HENRY 
ERNI,  A.M.,  M.D.,  Professor  of  Chemistry.  Second  Edition,  rewritten, 
enlarged  and  improved.  I2mo. £>3  oc 

FAIRBAIRN.— The  Principles  of  Mechanism  and  Machinery 

of  Transmission  • 

Comprising  the  Principles  of  Mechanism,  Wheels,  and  Pullevs, 
Strength  and  Proportions  of  Shafts,  Coupling  of  Shafts,  and  Engag- 
ing  and  Disengaging  Gear.  By  SIR  WILLIAM  FAIRBAIRN,  Bart 
C.  E.  Beautifully  illustrated  by  over  150  wood-cuts.  In  one 
volume.  I2mo #2.$c 

FLEMING. — Narrow  Gauge  Railways  in  America. 
A  Sketch  of  their  Rise,  Progress,  and   Success.     Valuable  Statistics 
as  to  Grades,  Curves,  Weight  of  Rail,  Locomotives,  Cars,  etc.     By 
HOWARD  FLEMING.     Illustrated,  8vo $i  oo 

FORSYTH.— Book  of   Designs  for  Headstones,   Mural,   and 

oth&f  Monuments : 

Containing  78  Designs.  By  JAMES  FORSYTH.  With  an  Introduction 
by  CHARLES  BGUTELL,  M.  A.  4  to.,  cloth  .  #5  OP 


HENRY   CAREY   BAIRD.&   CO.'S   CATALOGUE         '3 


FRANKEL— HOTTER.— A  Practical  Treatise  on  the  Manu* 

facture  of  Starch,  Glucose,  Starch-Sugar,  and  Dextrine: 
Based  on  the  German  of  LADISLAUS  VON  WAGNER,  Professor  in  the 
Royal  Technical  High  School,  Buda-Pest,  Hungary,  and  other 
authorities.  By  JULIUS  FRANKEL,  Graduate  of  the  Polytechnic 
School  of  Hanover.  Edited  by  ROBERT  H UTTER,  Chemist,  Practical 
Manufacturer  of  Starch-Sugar.  Illustrated  by  58  engravings,  cover- 
ing every  branch  of  the  subject,  including  examples  of  the  most 
Recent  and  Best  American  Machinery.  8vo.,  344  pp.  .  $3  50 

aARDNER. — The  Painter's  Encyclopaedia: 
Containing  Definitions  of  all  Important  Words  in  the  Art  of  Plain 
and  Artistic  Painting,  with  Details  of  Practice  in  Coach,  Carriage, 
Railway  Car,  House,  Sign,  and  Ornamental  Painting,  including 
Graining,  Marbling,  Staining,  Varnishing,  Polishing,  Lettering, 
Stenciling,  Gilding,  Bronzing,  etc.  By  F'RANKLIN  B.  GARDNER. 
158  Illustrations.  I2mo.  427  pp.  .  .  ._,.'.  $2.00 

GARDNER.— Everybody's  Paint  Book: 

A  Complete  Guide  to  the  Art  of  Outdoor  and  Indoor  Painting,  De- 
signed for  the  Special  Use  of  those  who  wish  to  do  their  own  work, 
and  consisting  of  Practical  Lessons  in  Plain  Painting,  Varnishing, 
Polishing,  Staining,  P?prr  Hanging,  Kalsomining,  etc.,  as  well  as 
Directions  for  Renovating  Furniture,  and  Hints  on  Artistic  Work  for 
Home  Decoration.  38  Illustrations.  I2mc.,  183  pp.  .  $1.00 

SEE. — The  Goldsmith's  Handbook : 

Containing  full  instructions  for  the  Alloying  and  Working  of  Gold, 
including  the  Art  of  Alloying,  Melting,  Reducing,  Coloring,  Col 
lecting,  and  Refining;  the  Processes  of  Manipulation,  Recovery  of 
Waste ;  Chemical  and  Physical  Properties  of  Gold ;  with  a  New 
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Rules  and  Recipes.  By  GEORGE  E.  GEE.  I2mo.  „  .  $1-7$ 

GEE. — The  Silversmith's  Handbook  : 

Containing  full  instructions  for  the  Alloying  and  Working  of  Silver, 
including  the  different  modes  of  Refinir'-  and  Melting  the  Metal ;  its 
Solders;  the  Preparation  of  Imitation  Alloys;  Methods  of  Manipula- 
tion; Prevention  of  Waste  ;  Instructions  for  Improving  and  Finishing 
the  Surface  of  the  Work;  together  with  other  Useful  Information  and 
Memoranda.  By  GEORGE  E.  GEE.  Illustrated.  I2mo.  $1.75 

GOTHIC  ALBUM  FOR  CABINET-MAKERS: 

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3RANT.—  A  Handbook  on  the  Teeth  of  Gears : 
Their  Curves,  Properties,  and  Practical  Construction.     By  GEORGE 
B.  GRANT.     Illustrated.     Third  Edition,  enlarged.     Svo.          $1  oo 

GREENWOOD.— Steel  and  Iron: 

Comprising  the  Practice  and  Theory  of  the  Several  Methods  Pur- 
sued in  their  Manufacture,  and  of  their  Treatment  in  the  Rolling. 
Mills,  the  Forge,  and  the  Foundry.  By  WILLIAM  HENRY  GREEN- 
WOOD, F.  C.  S.  With  97  Diagrams,  536  pages.  I2mo.  $2.00 


HENRY   CAREY    BA1RD   &   CO.'S   CATALOGUE. 


GREGORY.— Mathematics  for  Practical  Men : 

Adapted  to  the  Pursuits  of  Surveyors,  Architects,  Mechanics,  and 
Civil  Engineers.  By  OLINTHUS  GREGORY.  8vo.,  plates  $3.00 

GRISWOLD. — Railroad  Engineer's  Pocket  Companion  for  the 

Field: 

Comprising  Rules  for  Calculating  Deflection  Distances  and  Angles, 
Tangential  Distances  and  Angles,  and  all  Necessary  Tables  for  En 
gineers;  also  the  Art  of  Levelling  from  Preliminary  Survey  to  the 
Construction  of  Railroads,  intended  Expressly  for  the  Young  En- 
gineer, together  with  Numerous  Valuable  Rules  and  Examples.  By 
W.  GRISWOLD.  i2mo.,  tucks  •  •  ....  $i-75 

GRUNER. — Studies  of  Blast  Furnace  Phenomena: 

By  M.  L.  GRUNER,  President  of  the  General  Council  of  Mines  o5 
France,  and  lately  Professor  of  Metallurgy  at  the  Ecole  des  Mines. 
Translated,  with  the  author's  sanction,  with  an  Appendix,  by  L.  D. 
B.  GORDON,  F.  R.  S.  E.,  F.  G.  S.  8vo.  .  .  .  $2  50 

Hand-Book  of  Useful  Tables  for  the  Lumberman,  Farmet  and 

Mechanic: 

Containing  Accurate  Tables  of  Logs  Reduced  to  Inch  Board  Meas. 
ure,  Plank,  Scantling  and  Timber  Measure;  Wages  and  Rent,  by 
Week  or  Month;  Capacity  of  Granaries,  Bins  and  Cisterns;  Land 
Measure,  Interest  Tables,  with  Directions  for  Finding  the  Interest  on 
any  sum  at  4,  5,  6,  7  and  8  per  cent.,  and  many  other  Useful  Tables. 
32  mo.,  boards.  186  pages .25 

HASERICK.— The  Secrets  of  the  Art  of  Dyeing  Wool,  Cotton, 

and  Linen, 

Including  Bleaching  and  Coloring  Wool  and  Cotton  Hosiery  and 
Random  Yarns.  A  Treatise  based  on  Economy  and  Practice.  By 
E.  C.  HASERICK.  Illustrated  by  323  Dyed  Patterns  of  the  Yarn! 
or  fabrics.  8vo $7-5° 

HATS  AND  FELTING : 

A  Practical  Treatise  on  their  Manufacture.  By  a  Practical  Matte*. 
Illustrated  by  Drawings  of  Machinery,  etc.  8vo.  .  .  $1.25 

HOFFER. — A    Practical   Treatise   on   Caoutchouc  and   Gutta 

Percha, 

Comprising  the  Properties  of  the  Raw  Materials,  and  the  manner  r>r 
Mixing  and  Working  them ;  with  the  Fabrication  of  Vulcanized  and 
Hard  Rubbers,  Caoutchouc  and  Gutta  Percha  Compositions,  Water- 
proof Substances,  Elastic  Tissues,  the  Utilization  of  Wasic,  etc.,  t<, 
From  the  German  of  RAIMUND  HOFFER.  By  W.  T.  BRAIXNT. 
Illustrated  I2mo.  .  $2.50 

HAUPT.— Street  Railway  Motors: 

Wiih  Descriptions  and  Cost  of  Plants  and  Operation  of  the  Various 
Systems  now  in  Use.  I2mo.  .  .  .  .  ,  .  .  $1-75 


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HAUPT— RHAWN.— A  Move  for  Better  Roads: 

Fssays  on  Road-making  and  Maintenance  and  Road  Laws,  for 
which  Prizes  or  Honorable  Mention  were  Awarded  through  the 
University  of  Pennsylvania  by  a  Committee  of  Citizens  of  Philadel- 
phia, with  a  Synopsis  of  other  Contributions  and  a  Review  by  the 
Secretary,  LEWIS  M.  HAUPT,  A.  M.,  C.  E.;  also  an  Introduction  by 
WILLIAM  H.  RHAWN,  Chairman  of  the  Committee.  319  pages. 
8vo $2.00 

HUGHES. — American  Miller  and  Millwright's  Assistant: 
By  WILLIAM  CARTER  HUGHES.     I2mo $1.50 

HULME. — Worked  Examination  Questions  in  Plane  Geomet- 
rical Drawing  : 

For  the  Use  of  Candidates  for  the  Royal  Military  Academy,  Wool- 
wich;  the  Royal  Military  College,  Sandhurst;  the  Indian  Civil  En- 
gineering College,  Cooper's  Hill ;  Indian  Public  Works  and  Tele- 
graph Departments;  Royal  Marine  Lk'ht  Infantry;  the  Oxford  and 
Cambridge  Local  Examinations,  etc.  By  F.  EDWARD  HULME,  F.  L. 
S.,  F.  S.  A.,  Art-Master  Marlborough  College.  Illustrated  bv  300 
examples.  Small  quartc »  $2.50 

JER VIS.— Railroad  Property: 

A  Treatise  on  the  Construction  and  Management  of  Railways; 
designed  to  afford  useful  knowledge,  in  the  popular  style,  to  the 
holders  of  this  class  of  property ;  as  well  as  Railway  Managers,  Offi- 
cers, and  Agents.  By  JOHN  B.  JERVIS,  late  Civil  Engineer  of  the 
Hudson  River  Railroad,  Croton  Aqueduct,  etc.  i2mo.,  cloth  $2.oc 

KEENE. — A  Hand-Book  of  Practical  Gauging: 

For  the  Use  of  Beginners,  to  which  is  added  a  Chapter  on  Distilla- 
tion, describing  the  process  in  operation  at  the  Custom- House  for 
ascertaining  the  Strength  of  Wines.  By  JAMES  B.  KEENE,  of  H.  M. 
Customs.  8vo #1-25 

KELLEY.— Speeches,  Addresses,  and  Letters  on  Industrial  and 

Financial  Questions : 
By  HON.  WILLIAM  D.  KELLEY,  M.  C.     544  pages,  8vo.  .        #2.50 

KELLOGG.— A  New  Monetary  System  : 

The  only  means  of  Securing  the  respective  Rights  of  Labor  and 
Property,  and  of  Protecting  the  Public  from  Financial  Revulsions. 
By  EDWARD  KELLOGG.  Revised  from  his  work  on  "Labor  and 
other  Capital."  With  numerous  additions  from  his  m-nu^ript. 
Edited  by  MARY  KELLOGG  PUTNAM.  Fifth  edition.  To  which  i* 
added  a  Biographical  Sketch  of  the  Author.  One  volume,  I2mo. 

Paper  cover jjll.oo 

Bound  in  cloth I<25 

KEMLO.— Watch-Repairer's  Hand-Book : 
Beimr  a  Complete  Guide  to  the  Young  Beginner,  in  Taking  Apart, 
Putting  Together,  and  Thoroughly  Cleaning  the  English  Lever  and 
other  Foreign  Watches,  and  all  American  Watches.     By  F.  KEMLO, 
Practical  Watchmaker.     With  Illustrations.     I2mo.  .         $1.25 


16  HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

KENTISH.— A  Treatise  on  a  Box  of  Instruments, 
And  the  Slide  Ruie;  with  the  Theory  of  Trigonometry  and  Logs 
rithms,  including  Practical  Geometry,  Surveying,  Measuring  of  Tim 
ber,  Ca^k  and  Malt  Gauging,  Heights,  and  Distances.     By  THOMA' 
KENTISH.     In  one  volume.     I2mo.  .         .         .         .         $1.2$ 

KERL.— The  Assayer's  Manual: 

An  Abridged  Treatise  on  the  Docimastic  Examination  of  Ores,  and 
Furnace  and  other  Artirichl  Products.  By  BRUNO  KERL,  Prote;«sor 
in  the  Royal  School  of  Mines.  Translated  from  the  Gtrman  by 
WILLIAM  T.  BRANNT.  Second  American  edition,  edited  with  Ex- 
tensive Additions  by  F.  LYNWOOD  GARRISON,  Member  of  the 
American  Institute  of  Mining  Engineers,  etc.  Illustrated  by  87  en- 
gravings. 8vo #3.00 

KICK.— Flour  Manufacture. 

A  Treatise  on  Milling  Science  and  Practice.  By  FREDERICK  KICK 
Imperial  Regierungsrath,  Professor  of  Mechanical  Technology  in  tin. 
imperial  German  Polytechnic  Institute,  Prague.  Translated  from 
the  second  enlarged  and  revised  edition  with  supplement  by  H.  H. 
P.  POWLES,  Assoc.  Memb  Institution  of  Civil  Engineers.  Illustrated 
with  28  Plates,  and  167  Wood-cuts.  367  pages.  8vo.  .  #10.00 
KINGZETT.— The  History,  Products,  and  Processes  of  the 

Alkali  Trade  : 

Including  the  most  Recent  Improvements.     By  CHARLES  THOMAS 
K i  NGZETT,  Consulting  Chemist.    With  23  illustrations.    8vo.       $2.50 
KIRK. — The  Founding  of  Metals : 

A  Practical  Treatise  on  the  Melting  of  Iron,  with  a  Description  of  the 
Founding  of  Alloys;  also,  of  all  the  Metals  and  Mineral  Substances 
used  in  the  Art  of  Founding.  Collected  from  orginal  sources.  B) 
EDWARD  KIRK,  Practical  Foundryman  and  Chemist.  Illustrated, 
Third  edition.  8vo.  .  .  .  •  •  .  .  $>2.$C 

LANDRIN.— A  Treatise  on  Steel: 

Comprising  its  Theory,  Metallurgy,  Properties,  Practical  Working, 
and  Use.  By  M.  H.  C.  LANDRIN,  JR.,  Civil  Engineer.  Translated 
from  the  French,  with  Notes,  by  A.  A.  FESQUET,  Chemist  and  En 
gineer.  With  an  Appendix  on  the  Bessemer  and  the  Martin  Pro 
reuses  for  Manufacturing  Steel,  from  the  Report  of  Ab^am  S.  Hewitt 
United  States  Commissioner  to  the  Universal  Exposition,  Paris,  1867. 
I2IP.O.  . $3-OC 

LANGBEIN.— A  Complete  Treatise  on  the  Electro-Deposition 

of  Metals  : 
Translated   from  the  German,  with   Additions,  by  WM.  T.  BRANNT. 

125  illusirations.     8vo.      .         .         .     •     .     ?•'    .         .          .         $4.00 

LARDNER.— The  Steam-Engine  : 

for  the  Use  of  Beginners.     Illustrated.     I2mo  .         .         7X 

?-EHNER.— The  Manufacture  of  Ink: 

Comprising  the  Raw  Materials,  and  the  Preparation  of  Waiting, 
Copying  and  Hekiograph  Inks,  Safety  Inks,  Ink  Extracts  and  Pow- 
ders,  etc.  Translated  from  the  German  of  SiGMUND  LEHNER,  with 
additions  by  WILLIAM  T.  BRANNT.  Illustrated.  i2tno.  $2.00 


HENRY   CAREY    BAIRD   &   CO.'S   CATALOGUE.        17 

LARKIN. — The  Practical  Brass  and  Iron  Founder's  Guide: 
A  Concise  Treatise  on  Brass  Founding,  Moulding,  the  Metals  and 
their  Alloys,  etc.;  to  which  are  added  Recent  Improvements  in  the 
Manufacture  of  Iron,  Steel  by  the  Bessemer  Process,  etc.,  etc.  Bf 
TAMES  LARKIN,  lale  Conductor  of  the  Brass  Foundry  Department  in 
Reany,  Neafie  &  Co.'s  Penn  Works,  Philadelphia.  New  edition, 
revised,  with  extensive  additions.  I2mo.  .  .  .  $2.50 

LEROUX.— A    Practical     Treatise     on    the    Manufacture    of 

Worsteds  and  Carded  Yarns  : 

Comprising  Practical  Mechanics,  with  Rules  and  Calculations  applied 
to  Spinning;  Sorting,  Cleaning,  and  Scouring  Wools;  the  English 
and  French  Methods  of  Combing,  Drawing,  and  Spinning  Worsteds, 
and  Manufacturing  Carded  Yarns.  Translated  from  the  French  of 
CHARLES  LEROUX,  Mechanical  Engineer  and  Superintendent  of  a 
Spinning-Mill,  by  HORATIO  PAINE,  M.  D.,  and  A.  A.  FESQUET, 
Chemist  and  Engineer.  Illustrated  by  twelve  large  Plates.  To  which 
is  added  an  Appendix,  containing  Extracts  from  the  Reports  of  the 
International  Jury,  and  of  the  Artisans  selected  by  the  Committee 
appointed  by  the  Council  of  the  Society  of  Arts,  London,  on  Woolen 
and  Worsted  Machinery  and  Fabrics,  as  exhibited  in  the  Paris  UnU 
versai  Exposition,  1867.  8vo.  .....  $5.00 

LEFFEL. — The  Construction  of  Mill-Dams  : 
Comprising  also  the  BuMding  of  Race  and  Reservoir  Embankments 
and   Head-Gates,  the   Measurement  of  Streams,  Gauging  of  Water 
Supply,  etc.     By  JAMES  LEFFEL  &  Co.    Illustrated  by  58  engravings. 
8vo $2.50 

LESLIE.— Complete  Cookery: 

Directions  for  Cookery  in  its  Various  Branches.  By  Miss  LESLIE. 
Sixtieth  thousand.  Thoroughly  revised,  with  the  addition  of  New 
Receipts.  I2mo #1.50 

LE  VAN. — The  Steam  Engine  and  the  Indicator : 

Their  Origin  and  Progressive  Development ;  including  the  Most 
Recent  Examples  of-  Steam  and  Gas  Motors,  together  with  the  Indi- 
cator, its  Principles,  its  Utility,  and  its  Application.  By  WILLIAM 
BARNET  LE  VAN.  Illustrated  by  205  Engravings,  chiefly  of  Indi. 
cator-Cards.  469  pp.  8vo $4.00 

LIEBER. — Assayer's  Guide  : 

Or,  Practical  Directions  to  Assayers,  Miners,  and  Smelters,  for  the 
Tests  and  Assays,  by  Heat  and  by  Wet  Processes,  for  the  Ores  of  all 
the  principal  Metals,  of  Gold  and  Silver  Coins  and  Alloys,  and  of 
Coal,  etc.  By  OSCAR  M.  LIEBER.  Revised.  283  pp.  I2mo.  $1.50 

jLockwood's  Dictionary  of  Terms  : 

Used  in  the  Practice  of  Mechanical  Engineering,  embracing  those 
Current  in  the  Drawing  Office,  Pattern  Shop,  Foundry,  Fitting,  Turn- 
ing, Smith's  and  Boiler  Shops,  etc.,  etc.,  comprising  upwards  of  Six' 
Thousand  Definitions.  Edited  by  a  Foreman  Pattern  Maker,  author 
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i8         HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

LUKIN.— Amongst  Machines: 

Embracing  Descriptions  of  the  various  Mechanical  Appliances  used 
in  the  Manufacture  of  Wood,  Metal,  and  other  Substances.  I2mo. 

ii-rs 

LUKIN.— The  Boy  Engineers : 
What  They  Did,  and  How  They  Did  It.     With  30  plates.    I8mo. 

#i-75 

LUKIN.— The  Young  Mechanic  t 

Practical  Carpentry.  Containing  Directions  for  the  Use  of  all  kinds 
of  Tools,  and  for  Construction  of  Steam- Engines  and  Mechanical 
Models,  including  the  Art  of  Turning  in  Wood  and  Metal.  By  JOHN 
LUKIN,  Author  of  "The  Lathe  and  Its  Uses,"  etc.  Illustrated. 
I2mo $!-75 

MAIN  and  BROWN. — Questions  on  Subjects  Connected  with 

the  Marine  Steam -Engine : 

And  Examination  Papers;  with  Hints  for  their  Solution.  By 
THOMAS  J.  MAIN,  Professor  of  Mathematics,  Royal  'ttavai  College, 
and  THOMAS  BROWN,  Chief  Engineer,  R.  N.  I2mo.,  cloth  .  $1.00 

MAIN  and  BROWN. — The  Indicator  and  Dynamometer: 
With  their  Practical  Applications  to  the  Steam-Engine.     By  THOMAS 
J.  MAIN,   M.  A.  F.  R.,  Ass't    S.   Professor    Royal   Naval   College, 
Portsmouth,  and  THOMAS  BROWN,  Assoc.  Inst.  C.  E.,  Chief  Engineer 
R.  N.,  attached  to  the  R.  N.  College.     Illustrated.     8vo.  .         $1.00 

MAIN  and  BROWN.— The  Marine  Steam-Engine. 
By  THOMAS  J.  MAIN,  F.  R.  Ass't  S.  Mathematical  Professor  at  the 
Royal    Naval    College,   Portsmouth,   and    THOMAS    BROWN,   Assoc. 
Inst.  C.  E.,  Chief  Engineer  R.  N.     Attached  to  the  Royal  Naval 
College.     With  numerous  illustrations.     8vo. 

MAKINS.— A  Manual  of  Metallurgy: 

By  GEORGE  HOGARTH  MAKINS.  100  engravings.  Second  edition 
rewritten  and  much  enlarged.  I2mo.,  592  pages  .  .  $3-oo 

MARTIN.— Screw-Cutting  Tables,  for  the  Use  of  Mechanica) 

Engineers  : 

Showing  the  Proper  Arrangement  of  Wheels  for  Cutting  the  Threads 
of  Screws  of  any  Required  Pitch;  with  a  Table  for  Making  the  Uni- 
versal Gas-Pipe  Thread  and  Taps.  By  W.  A.  MARTIN,  Engineer. 
8vo 5c 

MICHELL.— Mine  Drainage: 

Being  a  Complete  and  Practical  Treatise  on  Direct-Acting  Under- 
ground Steam  Pumping  Machinery.  With  a  Description  of  a  large 
number  of  the  best  known  Engines,  their  General  Utility  and  ihe 
Special  Sphere  of  their  Action,  the  Mode  of  their  Application,  and 
their  Merits  compared  with  other  Pumping  Machinery.  By  STEPHEN 
MlCHELL.  Illustrated  by  137  engravings.  8vo.,  277  pages  .  $6.O6 

MOLESWORTH.— Pocket-Book    of    Useful     Formulae     and 

Memoranda  for  Civil  and  Mechanical  Engineers. 
By  GUILFORD  L.  MOLESWORTH,  Member  of  the  Institution  of  Civil 
Engineers,  Chief  Resident  Engineer  of  the  Ceylon  Railway.     Full- 
fluund  in  Pocket-book  form £1.0* 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.          19 

MOORE.— The  Universal  Assistant  and  the   Complete  Me- 
chanic : 

Containing  over  one  million  Industrial  Facts,  Calculations,  Receipts, 
Processes,  Trades  Secrets,  Rules,  Business  Forms,  Legal  Items,  Etc., 
in  every  occupation,  from  the  Household  to  the  Manufactory.  By 
R.  MOORE.  Illustrated  by  500  Engravings.  I2mo.  .  $2.50 

MORRIS. — Easy  Rules  for  the  Measurement  of  Earthworks: 
By  means  of  the  Prismoidal  Formula.  Illustrated  with  Numerout 
Wood-Cuts,  Problems,  and  Examples,  and  concluded  by  an  Exten- 
sive Table  for  finding  the  Solidity  in  cubic  yards  from  Mean  Areas. 
The  whole  being  adapted  for  convenient  use  by  Engineers,  Surveyors, 
Contractors,  and  others  needing  Correct  Measurements  of  Earthwork. 
By  ELWOOD  MORRIS,  C.  E.  8vo $1.50 

MAUCHLINE.— The  Mine  Foreman's  Hand-Book 

Of  Practical  and  Theoretical  Information  on  the  Opening,  Venti- 
lating, and  Working  of  Collieries.  Questions  and  Answers  on  Prac- 
tical and  Theoretical  Coal  Mining.  Designed  to  Assist  Students  and 
Others  in  Parsing  Examinations  for  Mine  Foremanships.  By 
ROBERT  MAUCHLINE,  Ex-Inspector  of  Mines.  A  New,  Revised  and 
Enlarged  Edition.  Illustrated  by  114  engrarings.  8vo.  337 

Pases #3.75 

NAPIER. — A  System  of  Chemistry  Applied  to  Dyeing. 

By  JAMES  NAPIER,  F.  C.  S.  A  New  and  Thoroughly  Revised  Edi* 
tion.  Completely  brought  up  to  the  present  state  of  the  Science, 
including  the  Chemistry  of  Coal  Tar  "Colors,  by  A.  A.  FESQUET, 
Chemist  and  Engineer.  With  an  Appendix  on  Dyeing  and  Calico 
Printing,  as  shown  at  the  Universal  Exposition,  Paris,  1867.  Illus- 
trated. 8vo.  422  pages $3-5o 

NEVILLE.— Hydraulic  Tables,  Coefficients,  and  Formulae,  foi 

finding   the   Discharge  of  Water   from    Orifices,   Notches, 

Weirs,  Pipes,  and  Rivers : 

Third  Edition,  with  Additions,  consisting  of  New  Formulae  for  the 
Discharge  from  Tidal  and  Flood  Sluices  and  Siphons;  general  infor- 
mation on  Rainfall,  Catchment-Basins,  Drainage,  Sewerage,  Wa;e» 
Supply  for  Towns  and  Mill  Power.  By  IOHN  NEVILLE,  C.  E.  M  R 
I.  A. ;  Fellow  of  the  Royal  Geological  Society  of  Ireland.  Thick^ 

I2mo $5.50 

NEWBERY.— Gleanings     from     Ornamental     Art    of     every 

style : 

Drawn  from  Examples  in  the  British,  South  Kensington,  Indian, 
Crystal  Palace,  and  other  Museums,  the  Exhibitions  of  1851  and 
1862,  and  the  best  P^nglish  and  Foreign  works.  In  a  series  of  ioa 
exquisitely  drawn  Plates,  containing  many  hundred  examples.  Bjf 

ROBERT  NEWBERY.    410. $12.50 

NICHOLLS.  -The  Theoretical  and  Practical  Boiler-Maker  and 

Engineer's  Reference  Book: 

Containing  a  variety  of  Useful  Information  for  Employers  of  Labor 
Foremen  and  Working  Boiler- Makers.  Iron,  Copper,  and  Tinsmiths 


20        HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 


Draughtsmen,  Engineers,  the  General  Steam-using  Public,  and  for  thfi 
Use  of  Science  Schools  and  Classes.  By  SAMUEL  NICHOLLS.  Illus- 
trated  by  sixteen  plates,  I2mo. $2.50 

NICHOLSON.— A  Manual  of  the  Art  of  Bookbinding: 

Containing  full  instructions  in  the  different  Branches  of  Forwarding, 
Gilding,  and  Finishing.  Also,  the  Art  of  Marbling  Book-edges  and 
Paper.  By  JAMES  B.  NICHOLSON.  Illustrated.  I2mo.,  cloth  $2.2$ 

NICOLLS.— The  Railway  Builder: 

A  Hand-Book  for  Estimating  the  Probable  Cost  of  American  Rail- 
way Construction  and  Equipment.  By  WILLIAM  J.  NICOLLS,  Civil 
Engineer.  Illustrated,  full  bound,  pocket-book  form  .  $2.00 

NORMANDY. — The  Commercial  Handbook  of  Chemical  An- 
alysis : 

Or  Practical  Instructions  for  the  Determination  of  the  Intrinsic  01 
Commercial  Value  of  Substances  used  in  Manufactures,  in  Trades, 
and  in  the  Arts.  By  A.  NORMANDY.  New  Edition,  Enlarged,  and 
to  a  great  extent  rewritten.  By  HENRY  M.  NOAD,  Ph.D.,  F.R.S., 
thick  I2mo gS-00 

NORRIS. — A  Handbook  fcr  Locomotive   Engineers  and  Ma- 

chimsts:  , 

Comprising  the  Proportions  and  Calculations  for  Constructing  Loco- 
motives; Manner  of  Setting  Valves;  Tables  of  Squares,  Cubes,  Areas, 
etc.,  etc.  By  SEPTIMUS  NORRIS,  M.  E.  New  edition.  Illustrated, 
I2mo $1.50 

NYSTROM. — A  New  Treatise  on  Elements  of  Mechanics : 
Establishing  Strict  Precision  in  the  Meaning  of  Dynamical  Terms : 
accompanied  with  an  Appendix  on  Duodenal  Arithmetic  and   Me 
trology.     By  JOHN  W.  NYSTROM,  C.  E.     Illustrated.     8vo.       $2.oc 

NYSTROM. — On  Technological  Education  and  the  Construc- 
tion of  Ships  and  Screw  Propellers : 

For  Naval  and  Marine  Engineers.  By  JOHN  W.  NYSTROM,  Inte 
Acting  Chief  Engineer,  U.  S.  N.  Second  edition,  revised,  with  addi- 
tional matter.  Illustrated  by  seven  engravings.  I2mo.  .  $1.50 

O'NEILL. — A  Dictionary  of  Dyeing  and  Calico  Printing: 

Containing  a  brief  account  of  all  rhe  Substances  and  Processes  in 
use  in  the  Art  of  Dyeing  and  Printing  Textile  Fabrics  ;  with  Practical 
Receipts  and  Scientific  Information.  By  CHARLES  O'NEILL,  Analy- 
tical Chemist.  To  which  is  added  an  Essay  on  Coal  Tar  Colors  and 
their  application  to  Dyeing  and  Calico  Printing.  By  A.  A.  FF.SO.UET> 
Chemist  and  Engineer.  With  an  appendix  on  Dyeing  and  Calico 
Printing,  as  shown  at  the  Universal  Exposition,  Paris,  1867-  8vo., 
491  pages $3.50 

ORTON. — Underground  Treasures-. 

How  and  Where  to  Find  Them.  A  Key  for  the  Ready  Determination 
of  all  the  Useful  Minerals  within  the  United  States.  By  JAMES 
ORTON,  A.M.,  Late  Professor  of  Natural  History  in  Vassar  College, 
N.  Y.;  Cor.  Mem.  of  the  Academy  of  Natural  Sciences,  Philadelphia, 
and  of  the  Lyceum  of  Natural  History,  New  York ;  author  of  the 
"Andes  and  the  Amazon."  etc.  A  New  Edition,  with  Additions. 
Illustrated  -  ,  - 1.0 


HENRY  CAREY  BArRD   &   CO.'S   CATALOGUE.       21 


OSBORN.— The  Prospector's  Field  Book  and  Guide : 

In  the  Search  for  and  the  Easy  Determination  of  Ores  and  Other 
Useful  Minerals.  By  Prof.  H.  S.  OSBORN,  LL.  D.,  Author  of 
"The  Metallurgy  of  Iron  and  Steel;"  "A  Practical  Manual  of 
Minerals,  Mines,  and  Mining."  Illustrated  by  44  Engravings. 
I2mo. $1.50 

OSBORN.— A  Practical  Manual  of  Minerals,  Mines  and  Min* 

ing: 

Comprising  the  Physical  Properties,  Geologic  Positions,  Local  Occur- 
rence and  Associations  of  the  Useful  Minerals ;  their  Methods  of 
Chemical  Analysis  and  Assay :  together  with  Various  Systems  of 
Excavating  and  Timbering,  Brick  and  Masonry  Work,  during  Driv- 
ing, Lining,  Bracing  and  other  Operations,  etc.  By  Prof.  H.  S. 
OSBORN,  LL.  D.,  Author  of  the  "  Metallurgy  of  Iron  and  Steel." 
Illustrated  by  171  engravings  from  original  drawings.  8vo.  $4.50 

OVERMAN.— Tlui  Manufacture  of  Steel : 

Containing  the  Practice  and  Principles  of  Working  and  Making  Steel. 
A  Handbook  for  Blacksmiths  and  Workers,  in  Steel  and  Iron,  Wagon 
Makers,  Die  Sinkers,  Cutlers,  and  Manufacturers  of  Files  and  Hard- 
ware, of  Steel  and  Iron,  and  for  Men  of  Science  and  Art.  By 
FREDERICK  OVERMAN,  Mining  Engineer,  Author  of  the  "  Manu- 
facture of  I»on,"  etc.  A  new,  enlarged,  and  revised  Edition.  By 
A.  A.  FESQLiCT,  Chemist  and  Engineer.  I2mo.  .  .  $1.50 

OVERMAN.— The  Moulder's  and  Founder's  Pocket  Guide  : 
A  Treatise  or.  Moulding  and  Founding  in  Green-sand,  Dry -sand,  Loam, 
and  Cement;  the  Moulding  of  Machine  Frames,  Mill-gear,  Hollow, 
ware,  Ornaments,  Trinkets,  Bells,  and  Statues;  Description  of  Moulds 
for  Iron,  Bronze,  Brass,  and  other  Metals;  Plaster  of  Paris,  Sulphur, 
Wax,  etc. ;  the  Construction  of  Melting  Furnaces,  the  Melting  and 
Founding  of  Metals ;  the  Composition  of  Alloys  and  their  Nature, 
etc.,  etc.  By  FREDERICK  OVERMAN,  M.  E.  A  new  Edition,  to 
which  is  added  a  Supplement  on  Statuary  and  Ornamental  Moulding, 
Ordnance,  Malleable  Iron  Castings,  etc.  By  A.  A.  FESQUET,  Chem- 
ist and  Engineer.  Illustrated  by  44  engravings.  I2mo.  .  $2.00 

PAINTER,  GILDER,  AND  VARNISHER'S  COMPANION, 
Containing  Rules  and  Regulations  in  everything  relating  to  the  Aril 
of  Painting,  Gilding,  Varnishing,  Glass-Staining,  Graining,  Marbling, 
Sign- Writing,  Gilding  on  Glas-s,  and  Coach  Painting  and  Varnishing; 
Tests  for  the  Detection  of  Adulterations  in  Oils,  Colors,  etc.;  and  a 
Statement  of  the  Diseases  to  which  Painters  are  peculiarly  liable,  with 
the  Simplest  and  Best  Remedies.  Sixteenth  Edition.  Revised,  with 
an  Appendix.  Containing  Colors  and  Coloring — Theoretical  ano 
Practical.  Comprising  descriptions  of  a  great  variety  of  Additional 
Pigments,  their  Qualities  and  Uses,  to  which  are  added,  Dryers,  and 
Modes  and  Operations  of  Painting,  etc.  Together  with  Chevreul'? 
Principles  of  Harmony  and  Contrast  of  Colors.  I2mo.  Cloth  $1.501 

PALLETT.— The  Miller's,  Millwright's,  and  Engineer's  Guide. 
By  HENRY  PALLETT.  Illustrated.  i2mo.  .  .  .  $2.0* 


22          HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

PERCY.— The  Manufacture  of  Russian  Sheet-Iron. 

By  JOHN  PERCY,  M.  D.,  F.  R.S.,  Lecturer  on  Metallurgy  at  the 
Royal  School  of  Mines,  and  to  The  Advance  Class  of  Artiller} 
Officers  at  the  Royal  Artillery  Institution,  Woolwich;  Author  of 
"  Metallurgy."  With  Illustrations.  8vo.,  paper  .  .  50  cts. 

PERKINS.— Gas  and  Ventilation  : 

Practical  Treatise  on  Gas  and  Ventilation.  With  Special  Relation 
to  Illuminating,  Heating,  and  Cooking  by  Gas.  Including  Scientific 
Helps  to  Engineer-students  and  others.  With  Illustrated  Diagrams. 
By  E.  E.  PERKINS.  I2mo.,  cloth $1.25 

PERKINS  AND  STOWS.— A  New  Guide  to  the  Sheet-iron 

and  Boiler  Plate  Roller : 

Containing  a  Series  of  Tables  showing  the  Weight  of  Slabs  and  Piles 
to  Produce  Boiler  Plates,  and  of  the  Weight  of  Piles  and  the  Sizes  of 
Bars  to  produce  Sheet-iron ;  the  Thickness  of  the  Bar  Gauge 
in  decimals ;  the  Weight  per  foot,  and  the  Thickness  on  the  Bar  or 
Wire  Gauge  of  the  fractional  parts  of  an  inch;  the  Weight  per 
sheet,  and  the  Thickness  on  the  Wire  Gauge  of  Sheet-iron  of  various 
dimensions  to  weigh  112  Ibs.  per  bundle;  and  the  conversion  of 
Short  Weight  into  Long  Weight,  and  Long  Weight  into  Short. 
Estimated  and  collected  by  G.  H.  PERKINS  and  J.  G-  STOWE.  $2.50 

POWELL— CHANCE— HARRIS,— The    Principles  of   Glass 

Making. 

By  HARRY  J.  POWELL,  B.  A.  Together  with  Treatises  on  Crown  and 
Sheet  Glass;  by  HENRY  CHANCE,  M.  A.  And  Plate  Glass,  by  H. 
G.  HARRIS,  Asso.  M.  Inst.  C.  E.  Illustrated  i8mo.  .  $1.50 

PROCTOR.— A  Pocket-Book  of  Useful  Tables  and  Formulae 

for  Marine  Engineers  : 

By  FRANK  PROCTOR.  Second  Edition,  Revised  and  Enlarged. 
Full -bound  pocket-book  form  .  .  .  ._...,  .  $1.50 

REGNAULT.— Elements  of  Chemistry: 

By  M.  V.  REGNAULT.  Translated  from  the  French  by  T.  FORREST 
BETTON,  M.  D.,  and  edited,  with  Notes,  by  JAMES  C.  BOOTH,  Melter 
and  Refiner  U.  S.  Mint,  and  WILLIAM  L.  FABER,  Metallurgist  and 
Mining  Engineer.  Illustrated  by  nearly  700  wood-engravings.  Com- 
prising nearly  1,500  pages.  In  two  volumes,  8vo.,  cloth  .  #7.50 

RICHARDS.— Aluminium : 

Its  History,  Occurrence,  Properties,  Metallurgy  and  Applications, 
including  its  Alloys.  By  JOSEPH  W.  RICHARDS,  A.  C.,  Chemist  and 
Practical  Metallurgist,  Member  of  the  Deutsche  Chemische  Gesell- 
schaft.  Illusr.  Third  edition,  enlarged  and  revised  (1895)  .  $6.00 

RIFFAULT,  VERGNAUD,  and  TOUSSAINT.— A  Practical 

Treatise  on  the  Manufacture  of  Colors  for  Painting : 
Comprising  the  Origin,  Definition,  and  Classification  of  Colors;  the 
Treatment  of  the  Raw  Materials ;  the  best  Formulae  and  the  Newest 
Processes  for  the  Preparation  of  every  description  of  Pigment,  and 
the  Necessary  Apparatus  and  Directions  for  its  Use;  Dryers;  the 
Testing.  Application,  and  Qualities  of  Paints,  etc.,  etc.  By  MM. 
RIFFAULT,  VERGNAUD,  and  TOUSSAINT.  Revised  and  Edited  by  M. 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.          23 


F.  MALEPEYRE.  Translated  from  the  French,  by  A.  A.  FESQUET, 
Chemist  and  Engineer.  Illustrated  by  Eighty  engravings.  In  one 
vol.,  8vo.,  659  pages $5.00 

ROPER. — A  Catechism  of  High-Pressure,  or  Non-Condensing 

Steam-Engines : 

Including  the  Modelling,  Constructing,  and  Management  of  Steam- 
Engines  and  Steam  Boilers.  With  valuable  illustrations.  By  STE- 
PHEN ROPER,  Engineer.  Sixteenth  edition,  revised  and  enlarged. 
i8mo.,  tucks,  gilt  edge $2.00 

ROPER. — Engineer's  Handy-Book: 

Containing  a  full  Explanation  of  the  Steam-Engine  Indicator,  and  its 
Use  and  Advantages  to  Engineers  and  Steam  Users.  With  Formula 
/or  Estimating  the  Power  of  all  Classes  of  Steam-Engines;  also, 
Facts,  Figures,  Questions,  and  Tables  for  Engineers  who  wish  to 
qualify  themselves  for  the  United  Stales  Navy,  the  Revenue  Service, 
the  Mercantile  Marine,  or  to  take  charge  of  the  Better  Class  of  Sta- 
tionary Steam-Engines.  Sixth  edition.  l6rao..  690  pages,  tucks, 
gilt  edge #3.50 

ROPER. — Hand-Book  of  Land  and  Marine  Engines  : 
Including  the  Modelling,  Construction,  Running,  and  Management 
of  Lane5  and  Marine  Engines  and  Boilers.     With  illustrations.     By 
STEPHEN  ROPER,  Engineer.    Sixth  edition.     I2mo.,tvcks,  gilt  edge. 

#3-50 
ROPER.— Hand-Book  of  the  Locomotive  : 

Including  the  Construction  of  Engines  and  Boilers,  and  the  Construc- 
tion, Management,  and  Running  of  Locomotives.  By  STEPHEN 
ROPER.  Eleventh  edition.  i8mo.,  tucks,  gilt  edge  .  $2.50 

ROPER.— Hand-Book  of  Modern  Steam  Fire-Engines. 
With  illustrations.     By  STEPHEN  ROPER,  Engineer.     Fourth  edition, 
I2mo.,  tucks,  gilt  edge $3-$c 

ROPER. — Questions  and  Answers  for  Engineers. 

This  little  book  contains  all  the  Questions  that  Engineers  will  be 
asked  when  undergoing  an  Examination  for  the  purpose  of  procuring 
Licenses,  and  they  are  so  plain  that  any  Engineer  or  Fireman  of  or 
dinary  intelligence  may  commit  them  to  memory  in  a  short  time.  By 
STEPHEN  ROPER,  Engineer.  Third  edition  .  .  #3.00 

ROPER. — Use  and  Abuse  of  the  Steam  Boiler. 
By  STEPHEN   ROPER,  Engineer.     Eighth  edition,  with  illustrations. 
i8mo.,  tucks,  gilt  edge       .......        $2.00 

ROSE. — The  Complete  Practical  Machinist : 

Embracing  Lathe  Work,  Vise  Work,  Drills  and  Drilling,  Taps  and 
Dies,  Hardening  and  Tempering,  the  Making  and  Use  of  Tools, 
Tool  Grinding,  Marking  out  Work,  etc.  By  JOSHUA  ROSE.  Illus- 
trated by  356  engravings.  Thirteenth  edition,  thoroughly  revised 
and  in  great  part  rewritten.  In  one  vol.,  I2mo.,  439  pages  $2.50 

ROSE. — Mechanical  Drawing  Self-Taught: 
Comprising  Instructions  in  the  Selection  and  Preparation  of  Drawing 
Instruments,  Elementary  Instruction  in  Practical  Mechanical  Draw 


24         HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 

ing,  together  with  Examples  in  Simple  Geometry  and  Elementary 
Mechanism,  including  Screw  Threads,  Gear  Wheels,  Mechanical 
Motions,  Engines  and  Boilers.  By  JOSHUA  ROSE,  M.  E.  Illustrated 
by  330  engravings.  8vo,  313  pages  ....  $4.00 

ROSE.— The  Slide- Valve  Practically  Explained: 

Embracing  simple  and  complete  Practical  Demonstrations  of  tlu 
operation  of  each  element  in  a  Slide-valve  Movement,  and  illustrat- 
ing  the  effects  of  Variations  in  their  Proportions  by  examples  care, 
fully  selected  from  the  most  recent  and  successful  practice.  By 
JOSHUA  ROSE,  M.  E.  Illustrated  by  35  engravings  .  $1.00 

ROSS. — The  Blowpipe  in  Chemistry,  Mineralogy  and  Geology: 
Containing  all  Known  Methods  of  Anhydrous  Analysis,  many  Work- 
ing Examples,  and  Instructions  for  Making  Apparatus.  By  LIEUT.- 
COLONEL  W.  A.  Ross,  R.  A.,  F.  G.  S.  With  120  Illustrations. 
I2mo.  .  .  .  .  ,»  .  .  .  .  .  $2.OO 

SHAW.— Civil  Architecture:. 

Being  a  Complete  Theoretical  and  Practical  System  of  Building,  con- 
taining  the  Fundamental  Principles  of  the  Art.  By  EDWARD  SHAW, 
Architect.  To  which  is  added  a  Treatise  on  Gothic  Architecture,  etc. 
By  THOMAS  W.  SILLOWAY  and  GEORGE  M.  HARDING,  Architects. 
The  whole  illustrated  by  102  quarto  plates  finely  engraved  on  copper. 
Eleventh  edition.  4to. $7*5° 

SHUNK. — A  Practical  Treatise  on  Railway  Curves  and  Loca- 
tion, for  Young  Engineers. 
By  W.  F.  SHUNK,  C.  E.    I2mo.    Full  bound  pocket-book  form  $2.00 

SLATER. — The  Manual  of  Colors  and  Dye  Wares. 

By  J.  W.  SLATER.     I2mo.  .         .         .         .         .         $3.00 

SLOAN. — American  Houses  : 

A  variety  of  Original  Designs  for  Rural  Buildings.  Illustrated  by 
26  colored  engravings,  with  descriptive  references.  By  SAMUEL 
SLOAN,  Architect.  8vo. $1.50 

SLOAN. — Homestead  Architecture  : 

C'jntami.:^  Forty  Designs  for  Villas,  Cottages,  and  Farm-houses,  with 
Essays  on  Style,  Construction,  Landscape  Gardening,  Furniture,  etc., 
etc.  illustrated  by  upwards  of  200  engravings.  By  SAMUEL  SLOAN, 
Architect.  8vo.  .  . .  ;•  -  .  .  .  .  $3-5O 
SLOANE.— Ho.re  Experiments  m  Science. 

By  T.  O'CONOR  SLC^NE,  E.  M.,  A.M.,  Fh.  D.  Illustrated  by  91 
engravings.  I2mo.  .  .  .  .  .  .  .  $1.50 

SMEATON.— Builder's  Pockfc:>  Companion : 

Containing  the  Elements  of  Building,  Surveying,  and  Architecture; 

with   Practical   Rules  and   Instructions  corrected  with  the  subject. 

By  A.  C.  SMEATON,  Civil  Engineer,  etc.     I2tno.       .         .        $1.50 
SMITH.— A  Manual  of  Political  Economy. 

By  E.  PESHINE  SMITH.    A  New  Edition,  to  which  is  added  a  full 

Index.     I2mo $i  25 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.          25 

SMITH. — Parks  and  Pleasure  -  Grounds  : 

Or  Practical  Notes  on  Country  Residences,  Villas,  Public  Parks,  and 
Gardens.  By  CHARLES  H.  J.  SMITH,  Landscape  Gardener  and 
Garden  Architect,  etc.,  etc.  I2mo.  ....  $2.00, 

SMITH. — The  Dyer's  Instructor : 

Comprising  Practical  Instructions  in  the  Art  of  Dyeing  Silk,  Cotton,> 
Wool,  and  Worsted,  and  Woolen  Goods ;  containing  nearly  800 
Receipts.  To  which  is  added  a  Treatise  on  the  Art  of  Padding;  an$ 
the  Printing  of  Silk  Warps,  Skeins,  and  Handkerchiefs,  and  the 
various  Mordants  and  Colors  for  the  different  styles  of  such  work, 
By  DAVID  SMITH,  Pattern  Dyer.  izmo.  .  .  .  $2.00 

SMYTH. — A  Rudimentary  Treatise  on  Coal  and  Coal-Mining. 
By  WARRINGTON  W.  SMYTH,  M.  A.,  F.  R.  G.,  President  R.  G.  S, 
of  Cornwall.  Fifth  edition,  revised  and  corrected.  With  numer- 
ous illustrations.  I2mo.  ......  $1.7$ 

SNIVELY.— Tables  for  Systematic  Qualitative  Chemical  Anal, 

ysis. 
By  JOHN  H.  SNIVELY,  Phr.  D.     8vo.         .         .         .        .        $1.00 

SNIVELY.— The  Elements  of  Systematic  Qualitative  chemical 

Analysis : 

A  Hand-book  for  Beginners.    By  JOHN  H.  SNIVELY,  Phr.  D.    i6mo. 

$2.00 

STOKES.— The  Cabinet  Maker  and  Upholsterer's  Companion: 
Comprising  the  Art  of  Drawing,  as  applicable  to  Cabinet  Work; 
Veneering,  Inlaying,  and  Buhl- Work;  the  Art  of  Dyeing  and  Stain- 
ing Wood,  Ivory,  Bone,  Tortoise-Shell,  etc.  Directions  for  Lacker- 
ing, Japanning,  and  Varnishing;  to  make  French  Polish,  Glues, 
Cements,  and  Compos'' .^ns;  with  numerous  Receipts,  useful  to  work 
men  generally.  Bv  STOKES.  Illustrated.  A  New  Edition,  with 
an  Appendix  upor  /ench  Polishing,  Staining,  Imitating,  Varnishing^ 
etc.,  etc.  I2mo  ........  $1.25 

STRENGTH  AND  OTHER  PROPERTIES  OF  METALS; 
Reports  of  Experiments  on  the  Strength  and  other  Properties  of 
Metals  for  Cannon.  With  a  Description  of  the  Machines  for  Testing 
Metals,  and  of  the  Classification  of  Cannon  in  service.  By  Officers 
of  the  Ordnance  Department,  U.  S.  Army.  By  authority  of  the  Secre- 
tary of  War.  Illustrated  by  25  large  steel  plates.  Quarto  .  $10.00 

SULLIVAN.— Protection  to  Native  Industry. 
By  Sir  EDWARD  SULLIVAN,  Baronet,  author  of  "  Ten  Chapters  on 
Social  Reforms."     8vo #1.00 

SULZ.— A  Treatise  on  Beverages  : 

Or  the  Complete  Practical  Bottler.  Full  instructions  for  Laboratory 
Work,  with  Original  Practical  Recipes  for  all  kinds  of  Carbonated 
Drinks,  Mineral  Waters,  Flavorings,  Extracts,  Syrups,  etc.  By 
CHAS  HERMAN  SULZ.  Technical  Chemist  and  Practical  Bottler 
Illustrated  by  428  Engr&viia&s.  8i#  '&?.  ^vo  .  .  #10.00 


26         HENRY  CAREY  BAIRt?  &  CO.'S  CATALOGUE. 

SYME. — Outlines  of  an  Industrial  Science. 
By  DAVID  SYME.     i2mo.          .        .  .        .        .        $2.00 

TABLES     SHOWING     THE     WEIGHT     OF     ROUND, 

SQUARE,  AND  FLAT  BAR  IRON,  STEEL,  ETC., 
By  Measurement.     Cloth  .         .         .         .         .         •  63 

TAYLOR.— Statistics  of  Coal : 

Including  Mineral  Bituminous  Substances  employed  in  Arts  and 
Manufactures;  with  their  Geographical,  Geological,  and  Commercial 
Distribution  and  Amount  of  Production  and  Consumption  on  the 
American  Continent.  With  Incidental  Statistics  of  the  Iron  Manu- 
facture. By  R.  C.  TAYLOR.  Second  edition,  revised  by  S.  S.  HALDE- 
MAN.  Illustrated  by  five  Maps  and  many  wood  engravings.  8vo., 
cloth $6,00 

TEMPLETON. — The  Practical  Examinator  on  Steam  and  the 

Steam -Engine : 

With  Instructive  References  relative  thereto,  arranged  for  the  Use  o? 
Engineers,  Students,  and  others.  By  WILLIAM  TEMPLETON,  En- 
gineer.  I2mo.  .  ...  .  .  .  .  .  $1.00 

THAUSING.— The  Theory  and  Practice  of  the  Preparation  of 

Malt  and  the  Fabrication  of  Beer: 

With  especial  reference  to  the  Vienna  Process  of  Brewing.  Elab- 
orated from  personal  experience  by  JULIUS  E.  THAUSING,  Professor 
at  the  School  for  Brewers,  and  at  the  Agricultural  Institute,  Modling, 
near  Vienna.  Translated  from  the  German  by  WILLIAM  T.  BRANNT, 
Thoroughly  and  elaborately  edited,  with  much  American  matter,  and 
according  to  the  latest  and  most  Scientific  Practice,  by  A.  SCHWARZ 
and  DR.  A.  H.  BAUER.  Illustrated  by  140  Engravings.  8vo.,  Siq 
pages £10.00 

THOMAS. — The  Modern  Practice  of  Photography : 
By  R.  W.  THOMAS,  F.  C.  S.    8vo.  ....  25 

THOMPSON.— Political  Economy.     With  Especial  Reference 

to  the  Industrial  History  of  Nations  : 

By  ROBERT  E.  THOMPSON,  M.  A.,  Professor  of  Social  Science  in  the 
University  of  Pennsylvania.  I2mo.  .  ;  ;  .  .  $1.50 

THOMSON.— Freight  Charges  Calculator: 
By  ANDREW  THOMSON,  Freight  Agent.     241110.        .        .        $1.25 

TURNER'S  (THE)  COMPANION: 

Containing  Instructions  in  Concentric,  Elliptic,  and  Eccentric  Turn, 
ing;  also  various  Plates  of  Chucks,  Tools,  and  Instruments;  and 
Directions  for  using  the  Eccentric  Cutter,  Drill,  Vertical  Cutter,  and 
Circular  Rest;  with  Patterns  and  Instructions  for  working  them. 
I2mo $1.25 

TURNING  :   Specimens  of  Fancy  Turning   Executed  on  the 

Hand  or  Foot- Lathe : 

With  Geometric,  Oval,  and  Eccentric  Chucks,  and  Elliptical  Cutting 
Frame.  By  an  Amateur.  Illustrated  by  30  exquisite  Photographs. 
4to. •  m  >00 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.          27 

VAILE. — Galvanized- Iron  Cornice-Worker's  Manual  : 
Containing  Instructions  in  Laying  out  the  Different  Mitres,  and 
Making  Patterns  for  all  kinds  of  Plain  and  Circular  Work.  Also, 
Tables  of  Weights,  Areas  and  Circumferences  of  Circles,  and  other 
Matter  calculated  to  Benefit  the  Trade.  By  CHARLES  A.  VAILE. 
Illustrated  by  twenty-one  plates.  4to $5.00 

VILLE.— On  Artificial  Manures  : 

Their  Chemical  Selection  and  Scientific  Application  to  Agriculture. 
A  series  of  Lectures  given  at  the  Experimental  Farm  at  Vincennes, 
during  1867  and  1874-75.  By  M.  GEORGES  VILLE.  Translated  and 
Edited  by  WILLIAM  CROOKES,  F.  R.  S.  Illustrated  by  thirty-one 
engravings.  8vo.,  450  pages $6.00 

VILLE. — The  School  of  Chemical  Manures  : 
Or,  Elementary  Principles  in  the  Use  of  Fertilizing  Agents.     From 
the  French  of  M.  GEO.  VILLE,  by  A.  A.  FESQUET,  Chemist  and  En- 
gineer.     With  Illustrations.     I2mo.  ....         $1.25 

VOGDES. — The  Architect's  and  Builder's  Pocket- Companion 

and  Price-Book : 

Consisting  of  a  Shoit  but  Comprehensive  Epitome  of  Decimals,  Duo- 
decimals, Geometry  and  Mensuration ;  with  Tables  of  United  States 
Measures,  Sizes,  Weights,  Strengths,  etc.,  of  Iron,  Wood,  Stone, 
Brick,  Cement  and  Concretes,  Quantities  of  Materials  in  given  Sizes 
and  Dimensions  of  Wood,  Brick  and  Stone;  and  full  and  complete 
Bilis  of  Prices  for  Carpenter's  Work  and  Painting;  also,  Rules  for 
Computing  and  Valuing  Brick  and  Brick  Work,  Stone  Work,  Paint- 
ing, Plastering,  with  a  Vocabulary  of  Technical  Terms,  etc.  By 
FRANK  W.  VOGDES,  Architect,  Indianapolis,  Ind.  Enlarged,  revised, 
and  corrected.  In  one  volume,  368  pages,  full-bound,  pocket-book 

form,  gilt  edges #2.00 

Cloth         .  1.50 

VAN  CLEVE. — The  English  and  American  Mechanic : 

Comprising  a  Collection  of  Over  Three  Thousand  Receipts,  Rules, 
and  Tables,  designed  for  the  Use  of  every  Mechanic  and  Manufac- 
turer. By  B.  FRANK  VAN  CLEVE.  Illustrated.  500  pp.  12010.  $2.00 

WAHNSCHAFFE.— A  Guide  to  the  Scientific  Examination 

of  Soils: 

Comprising  Select  Methods  of  Mechanical  and  Chemical  Analysis 
and  Physical  Investigation.  Translated  from  the  German  of  Dr.  F. 
WAHNSCHAFFE.  With  additions  by  WILLIAM  T.  BRANNT.  Illus- 
trated by  25  engravings.  I2mo.  177  pages  .  .  .  $1.50 

WALL. — Practical  Graining : 

With  Descriptions  of  Colors  Employed  and  Tools  Used.  Illustrated 
by  47  Colored  Plates,  Representing  the  Various  Woods  Used  '• 
Interior  Finishing.  By  WILLIAM  E.  WALL.  8vo.  .  $2.50 

WALTON.— Coal-Mining  Described  and  Illustrated: 

By  THOMAS  H.  WALTON,  Mining  Engineer.  Illustrated  by  24  ?arge 
and  elaborate  Plates,  after  Actual  Workings  and  Apparatus.  J»5.oc 


28         HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE. 


WARE. — The  Sugar  Beet. 

Including  a  History  of  the  Beet  Sugar  Industry  in  Europe,  Varieties 
of  the  Sugar  Beet,  Examination,  Soils,  Tillage,  Seeds  and  Sowing, 
Yield  and  Cost  of  Cultivation,  Harvesting,  Transportation,  Conserva- 
tion, Feeding  Qualities  of  the  Beet  and  of  the  Pulp,  etc.  By  LEWH 
S.  WARE,  C.  E.,  M.  E.  Illustrated  by  ninety  engravings.  8vo. 

#4.00 
WARN. — The  Sheet-Metal  Worker's  Instructor: 

For  Zinc,  Sheet-Iron,  Copper,  and  Tin-Plate  Workers,  etc.  Contain- 
ing  a  selection  of  Geometrical  Problems ;  also,  Practical  and  Simple 
Rules  for  Describing  the  various  Patterns  required  in  the  different 
branches  of  the  above  Trades.  By  REUBEN  H.  WARN,  Practical 
Tin-Plate  Worker.  To  which  is  added  an  Appendix,  containing 
Instructions  for  Boiler- Making,  Mensuration  of  Surfaces  and  Solids, 
Rules  for  Calculating  the  Weights  of  different  Figures  of  Iron  and 
Steel,  Tables  of  the  Weights  of  Iron,  Steel,  etc.  Illustrated  by  thirty- 
two  Plates  and  thirty-seven  Wood  Engravings.  8vo.  .  $3.00 

WARNER. — New  Theorems,  Tables,  and  Diagrams,  for  the 
Computation  of  Earth-work : 

Designed  for  the  use  of  Engineers  in  Preliminary  and  Final  Estimates^ 
of  Students  in  Engineering,  and  of  Contractors  and  other  non-profes. 
sional  Computers.  In  two  parts,  with  an  Appendix.  Part  I.  A  Prac- 
tical Treatise;  Part  II.  A  Theoretical  Treatise,  and  the  Appendix. 
Containing  Notes  to  the  Rules  and  Examples  of  Part  I.;  Explana- 
tions of  the  Construction  of  Scales,  Tables,  and  Diagrams,  and  a 
Treatise  upon  Equival-ent  Square  Bases  and  Equivalent  Level  Heights. 
The  whole  illustrated  by  numerous  original  engravings,  comprising 
explanatory  cuts  for  Definitions  and  Problems,  Stereometric  Scales 
and  Diagrams,  and  a  series  of  Lithographic  Drawings  from  Models ; 
Showing  all  the  Combinations  of  Solid  Forms  which  occur  in  Railroad 
Excavations  and  Embankments.  By  JOHN  WARNER,  A.  M.,  Mining 
and  Mechanical  Engineer.  Illustrated  by  14  Plates.  A  new,  revised 
and  improved  edition.  8vo. $4-OC 

WATSON.— A  Manual  of  the  Hand-Lathe  : 

Comprising  Concise  Directions  for  Working  Metals  of  all  kinds, 
Ivory,  Bone  and  Precious  Woods;  Dyeing,  Coloring,  and  French 
Polishing;  Inlaying  by  Veneers,  and  various  methods  practised  to 
produce  Elaborate  work  with  Dispatch,  and  at  Small  Expense.  Bjr 
EGBERT  P.  WATSON,  Author  of  "  The  Modern  Practice  of  American 
Machinists  and  Engineers."  Illustrated  by  78  engravings.  $1.50 

WATSON. — The  Modern  Practice  of  American  Machinists  and 
Engineers 

Including  the  Construction,  Application,  and  Use  of  Drills,  Latiie 
Tools,  Cutters  for  Boring  Cylinders,  and  Hollow-work  generally,  with 
the  most  Economical  Speed  for  the  same;  the  Results  verified  b) 
Actual  Practice  at  the  Lathe,  the  Vise,  and  on  the  Floor.  Togethe* 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE.          2c 

with  Work»W»p  Management,  Economy  of  Manufacture,  the  Steam 
Engine,  Boilers,  Gears,  Belting,  etc.,  etc.  By  EGBERT  P.  WATSON, 
Illustrated  by  eighty-six  engravings.  I2mo.  .  .  .  $2.50 

WATSON.— The  Theory  and  Practice  of  the  Art  of  Weaving 

by  Hand  and  Power  • 

With  Calculations  and  Tables  for  the  Use  of  those  connected  with  the 
Trade.  By  JOHN  WATSON,  Manufacturer  and  Practical  Machine- 
Maker.  Illustrated  by  large  Drawings  of  the  best  Power  Looms. 
8vo.  .  #6.00 

WATT.— The  Art  of  Soap  Making: 

A  Practical  Hand-book  of  the  Manufacture  of  Hard  and  Soft  Soaps, 
Toilet  Soaps,  etc.,  including  many  New  Processes,  and  a  Chapter  on 
the  Recovery  of  Glycerine  from  Waste  Leys.  By  ALEXANDER 
WATT.  111.  I2mo.  .......  $3.00 

WEATKERLY. — Treatise  on  the  Art  of  Boiling  Sugar,  Crys* 

tailizing,  Lozenge-making,  Comfits,  Gum  Goods, 
And  other  processes  for  Confectionery,  etc.,  in  which  are  explained, 
in  an  easy  and  familiar  manner,  the  various  Methods  of  Manufactur- 
ing every  Description  of  Raw  and  Refined  Sugar  Goods,  as  sold  by 
Confectioners  and  others.     I2mo $i-5G 

WIGHT  WICK.— Hints  to  Young  Architects: 
Comprising  Advice  to  those  who,  while  yet  at  school,  are  destined 
to  the  Proiession;  to  such  as,  having  passed  their  pupilage,  are  about 
to  travel ;  and  to  those  who,  having  completed  their  education,  are 
about  to  practise.  Together  with  a  Model  Specification  involvii.g  * 
great  variety  of  instructive  and  suggestive  matter.  By  GEORGB 
WlGHTWlCK,  Architect.  A  new  edition,  revised  and  considerably 
enlarged ;  comprising  Treatises  on  the  Principles  of  Construction 
and  Design.  By  G.  HUSKISSON  GUILLAUME,  Architect.  Numerous 
Illustrations.  One  vol.  121110 $2.00 

W  ILL.— Tables  of  Qualitative  Chemical  Analysis. 

With  an  Introductory  Chapter  on  the  Course  of  Analysis.  By  Pro- 
fessor HEINRICH  WILL,  of  Giessen,  Germany.  Third  American, 
from  the  eleventh  German  edition.  Edited  by  CHARLES  F.  HIMES 
Ph.  D.,  Professor  of  Natural  Science,  Dickinson  College,  Carlisle,  Pa 
8vo.  .  .  •  .  ...  .  .  .  $1-50 

WILLIAMS.— On  Heat  and  Steam: 

Embracing  New  Views  of  Vaporization,  Condensation,  and  Explr, 
sion.  By  CHARLES  WYE  WILLIAMS,  A.  I.  C.  E.  Illustrated  8vo. 

#2.50 

WILSON.— A  Treatise  on  Steam  Boilers  : 

Their  Strength,  Construction,  and  Economical  Working.  By  RoBERt 
WILSON.  Illustrated  I2mo #2.50 

V\  ILSON. — First  Principles  of  Political  Economy: 
With  Reference  to  Statesmanship  and  the  Progress  of  Civilization. 
By  Professor  W.  D.  WILSON,  of  the  Cornell  University.     A  new  aixl 
revised  edition.     I2mo. $1-5° 


•<o        HENRY   CAREY   BAIRD   &   CO.'S  CATALOGUE. 

WOHLER.— A  Hand-Book  of  Mineral  Analysis  : 

By  F.  WOHLER,  Professor  of  Chemistry  in  the  University  of  Gottin- 
gen.  Edited  by  HENRY  B.  NASON,  Professor  of  Chemistry  in  the 
Renssalaer  Polytechnic  Institute,  Troy,  New  York.  Illustrated. 
I2mo $2.50 

WORSSAM.— On  Mechanical  Saws: 

From  the  Transactions  of  the  Society  of  Engineers.  1869.  By  S.  W. 
WORSSAM,  JR.  Illustrated  by  eighteen  large  plates.  8vo.  £2.50 

RECENT   ADDITIONS. 

BRANNT. — Varnishes,  Lacquers,  Printing  Inks  and  Sealing - 
Waxes : 

Their  Raw  Materials  and  their  Manufacture,  to  which  is  added  the 
Art  of  Varnishing  and  Lacquering,  including  the  Preparation  of  Put- 
ties and  of  Stains  for  Wood,  Ivory,  Bone,  Horn,  and  Leather.  By 
WILLIAM  T.  BRANNT.  Illustrated  by  39  Engravings,  338  pages. 

i2tno.      . $3.00 

BRANNT — The  Practical  Scourer  and  Garment  Dyer: 

Comprising  Dry  or  Chemical  Cleaning;  the  Art  of  Removing  Stains; 
Fine  Washing;  Bleaching  and  Dyeing  of  Straw  Hats,  Gloves,  and 
Feathers  of  all  kinds;  Dyeing  of  Worn  Clothes  of  all  fabrics,  in- 
eluding  Mixed  Goods,  by  One  Dip;  and  the  Manufacture  of  Soaps 
and  Fluids  for  Cleansing  Purposes.  Edited  by  WILLIAM  T.  BRANNT, 
Editor  of  "The  Techno-Chemical  Receipt  Book."  Illustrated. 
203  pages.  I2mo.  .  .  ...  .  .  $2.00 

BRANNT.— Petroleum . 

Its  History,  Origin,  Occurrence,  Production,  Physical  and  Chemical 
Constitution,  Technology,  Examination  and  Uses;  Together  with 
the  Occurrence  and  Uses  of  Natural  Gas.  Edited  chiefly  from  the 
German  of  Prof.  Hans  Hoefer  and  Dr.  Alexander  Veith,  by  WM. 
T.  BRANNT.  Illustrated  by  3  Plates  and  284  Engravings.  743  pp. 
8vo.  $7.50 

BRANNT.— A  Practical  Treatise  on  the  Manufacture  of  Vine- 
gar and  Acetates,  Cider,  and  Fruit- Wines  : 
Preservation  of  Fruits  and  Vegetables  by  Canning  and  Evaporation ; 
Preparation  of  Fruit-Butters,  Jellies,  Marmalades,  Catchups,  Pickles, 
Mustards,  etc.  Edited  from  various  sources.  By  WILLIAM  T. 
BRANNT.  Illustrated  by  79  Engravings.  479  pp.  8vo.  $5.00 

BRANNT.— The  Metal  Worker's    Handy-Book   of  Receipts 
and  Processes : 

Being  a  Collection  of  Chemical  Formulas  and  Practical  Manipula- 
tions for  the  working  of  all  Metals;  including  the  Decoration  and 
Beautifying  of  Articles  Manufactured  therefrom,  as  well  as  then- 
Preservation.  Edited  from  various  sources.  By  WILLIAM  T. 
BRANNT.  Illustrated.  i2mo.  $2.50 


HENRY  CAREY  BA1RD  &  CO.'S  CATALOGUE.       3I 

DEITE.— A  Practical  Treatise  on  the  Manufacture  cf  Per- 

fumery : 

Comprising  directions  for  making  all  kinds  of  Perfumes,  Sachet 
Powders,  Fumigating  Materials,  Dentifrices,  Cosmetics,  etc.,  with  a 
full  account  of  the  Volatile  Oils,  Balsams,  Resins,  and  other  Natural 
and  Artificial  Perfume-substances,  including  the  Manufacture  of 
Fruit  Ethers,  and  tests  of  their  purity.  By  Dr.  C.  DEITE,  assisted 
by  L.  BORCHERT,  F.  EICHBAUM,  E.  KUGLER,  H.  TOEFFNER,  and 
other  experts.  From  the  German,  by  WM.  T.  BRANNT.  28  Engrav- 
ings. 358  pages.  8vo. $3.00 

EDWARDS. — American    Marine  Engineer,    Theoretical   and 

Practical : 

With  Examples  of  the  latest  and  most  approved  American  Practice. 
By  EMORY  EDWARDS.  85  illustrations.  I2mo.  .  .  $2.50 

EDWARDS.— goo    Examination   Questions  and   Answers: 

For  Engineers  and   Firemen   (Land  and  Marine)  who  desire  to  ob- 
tain a  United  States  Government  or  State  License.     Pocket-book 
form,  gilt  edge          ........        $1.50 

POSSELT. — Technology  of  Textile  Design : 

Being  a  Practical  Treatise  on  the  Construction  and  Application  of 
Weaves  for  all  Textile  Fabrics,  with  minute  reference  to  the  latest 
Inventions  for  Weaving.  Containing  also  an  Appendix,  showing 
the  Analysis  and  giving  the  Calculations  necessary  for  the  Manufac. 
tuie  of  the  various  Textile  Fabrics.  By  E.  A.  POSSELT,  Head 
Master  Textile  Department,  Pennsylvania  Museum  and  School  of 
Industrial  Art,  Philadelphia,  with  over  looo  illustrations.  292 
pages.  410 $5-°° 

POSSELT. — The  Jacquard  Machine  Analysed  and  Explained: 
With  an  Appendix  on  the  Preparation  of  Jacquard  Cards,  and 
Practical  Hints  to  Learners  of  Jacquard  Designing.  By  E.  A. 
POSSELT.  With  230  illustrations  and  numerous  diagrams.  127  pp. 
4to $3.00 

POSSELT.— The  Structure  of  Fibres,  Yarns  and  Fabrics: 
Being  a  Practical  Treatise  for  the  Use  of  all  Persons  Employed  in 
the  Manufacture  of  Textile  Fabrics,  containing  a  Description  of  the 
Growth  and  Manipulation  of  Cotton,  Wool.  Worsted,  Silk.  Flax, 
Jute,  Ramie,  China  Grass  and  Hemp,  and  Dealing  with  all  Manu- 
facturers' Calculations  for  Every  Class  of  Material,  also  Giving 
Minute  Details  for  the  Structure  of  all  kinds  of  Textile  Fabrics,  and 
an  Appendix  of  Arithmetic,  specially  adapted  for  Textile  Purposes. 
By  E.  A.  POSSELT.  Over  400  Illustrations,  quarto.  .  $10.00 

RICH. — Artistic  Horse-Shoeing: 

A  Practical  and  Scientific  Treatise,  giving  Improved  Methods  of 
Shoeing,  with  Special  Directions  for  Shaping  Shoes  to  Cure  Different 
Diseases  of  the  Foot,  and  for  the  Correction  of  Faulty  Action  in 
Trotters.  By  GEORGE  E.  RICH.  62  Illustrations.  153  pages. 
I2mo .  .  .  .  $1.00 


32       HENRY   CAREY   BAIRD  &  CO.'S  CATALOGUE. 

RICH ARDSON.— Practical  Blacksmithing : 

A  Collection  of  Articles  Contributed  at  Different  Times  by  Skilled 
Workmen  to  the  columns  of  "  The  Blacksmith  and  Wheelwright," 
and  Covering  nearly  the  Whole  Range  of  Blacksmithing,  from  the 
Simplest  Job  of  Work  to  some  of  the  Most  Complex  Forgings. 
Compiled  and  Edited  by  M.  T.  RICHARDSON. 

Vol.  I.  210  Illustrations.  224  pages.  I2mo.  .  .  $1.00 
Vol.  IT.  230  Illustrations.  262  pages.  I2mo.  .  .  $1.00 
Vol.  III.  390  Illustrations.  307  pages.  I2mo.  .  .  $1.00 
Vol.  IV.  226  Illustrations.  276  pages.  I2mo.  .  .  $1.00 

RICHARDSON  —The  Practical  Horseshoer: 
Being  a  Collection  of  Articles  on  Horseshoeing  in  all  its  Branches 
which  have  appeared  from  time  to  time  in  the  columns  of  "  1  he 
Blacksmith  and  Wheelwright,"  etc.     Compiled  and  edited  by  M.  T. 
RICHARDSON.     174  illustrations.       .....        jjSi.oo 

ROPER. — Instructions    and    Suggestions    for   Engineers   and 

Firemen : 
By  STEPHEN  ROPER,  Engineer.     i8mo.     Morocco        .        $2.00 

ROPER. — The  Steam  Boiler:  Its  Care  and  Management: 
By  STEPHEN  ROPER,  Engineer.     I2mo.,  tuck,  gilt  edges.         $2.00 

ROPER. — The  Young  Engineer's  Own  Book : 

Containing  an  Explanation  of  the  Principle  and  Theories  on  which 
the  Steam  Engine  as  a  Prime  Mover  is  Based.  By  STEPHEN  ROPER, 
Engineer.  160  illustrations,  363  pages.  i8mo.,  tuck  .  $3.00 

ROSE. — Modern  Steam -Engines: 

An  Elementary  Treatise  upon  the  Steam-Engine,  written  in  Plain 
language ;  for  Use  in  the  Workshop  as  well  as  in  the  Drawing  Office. 
Giving  Full  Explanations  of  the  Construction  of  Modern  Stearrw 
Engines :  Including  Diagrams  showing  their  Actual  operation.  To- 
gether with  Complete  but  Simple  Explanations  of  the  operations  of 
Various  Kinds  of  Valves,  Valve  Motions,  and  Link  Motions,  etc., 
thereby  Enabling  the  Ordinary  Engineer  to  clearly  Understand  the 
Principles  Involved  in  their  Construction  and  Use,  and  to  Plot  out 
their  Movements  upon  the  Drawing  Board.  By  JOSHUA  ROSE.  M.  E. 
Illustrated  by  422  engravings.  Revised.  358  pp.  .  .  $6.00 

ROSE. — Steam  Boilers: 

A  Practical  Treatise  on  Boiler  Construction  and  Examination,  for  the 
Use  of  Practical  Boiler  Makers,  Boiler  Users,  and  Inspectors;  and 
embracing  in  plain  figures  all  the  calculations  necessary  in  Designing 
or  Classifying  Steam  Boilers.  By  JOSHUA  ROSE,  M.  E.  Illustrated 
by  73  engravings.  250  pages.  8vo $2.50 

BCHRIBER.— The  Complete  Carriage  and  Wagon  Painter: 
A  Concise  Compendium  of  the  Art  of  Painting  Carriages,  Wagons, 
and  Sleighs,  embracing  Full  Directions  in  all  the  Various  Branches, 
including  Lettering,  Scrolling,  Ornamenting,  Striping,  Varnishing, 
and  Coloring,  with  numerous  Recipes  for  Mixing  Color*.  73  Illus- 
trations. 177  pp.  i2mo $1.00 


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